Shannon’s information theory has been a popular component of first-order cybernetics. It quantifies information transmitted in terms of the number of times a sent symbol is received as itself, or as another possible symbol. Sent symbols were events and received symbols were outcomes. Garner and Hake reinterpreted Shannon, describing events and outcomes as categories of a stimulus attribute, so as to quantify the information transmitted in the psychologist’s category (or absolute judgment) experiment. There, categories are represented by specific stimuli, and (...) the human subject must assign those stimuli, singly and in random order, to the categories that they represent. Hundreds of computations ensued of information transmitted and its alleged asymptote, the sensory channel capacity. The present paper critically re-examines those estimates. It also reviews estimates of memory capacity from memory experiments. It concludes that absolute judgment is memory-limited and that channel capacities are actually memory capacities. In particular, there are factors that affect absolute judgment that are not explainable within Shannon’s theory, factors such as feedback, practice, motivation, and stimulus range, as well as the anchor effect, sequential dependences, the rise in information transmitted with the increase in number of stimulus dimensions, and the phenomena of masking and stimulus duration dependence. It is recommended that absolute judgments be abandoned, because there are already many direct estimates of memory capacity. (shrink)

Purpose – The purpose of this paper is to examine the popular “information transmitted” interpretation of absolute judgments, and to provide an alternative interpretation if one is needed. Design/methodology/approach – The psychologists Garner and Hake and their successors used Shannon’s Information Theory to quantify information transmitted in absolute judgments of sensory stimuli. Here, information theory is briefly reviewed, followed by a description of the absolute judgment experiment, and its information theory analysis. Empirical channel capacities are scrutinized. A remarkable coincidence, the (...) similarity of maximum information transmitted to human memory capacity, is described. Over 60 representative psychology papers on “information transmitted” are inspected for evidence of memory involvement in absolute judgment. Finally, memory is conceptually integrated into absolute judgment through a novel qualitative model that correctly predicts how judgments change with increase in the number of judged stimuli. Findings – Garner and Hake gave conflicting accounts of how absolute judgments represent information transmission. Further, “channel capacity” is an illusion caused by sampling bias and wishful thinking; information transmitted actually peaks and then declines, the peak coinciding with memory capacity. Absolute judgments themselves have numerous idiosyncracies that are incompatible with a Shannon general communication system but which clearly imply memory dependence. Research limitations/implications – Memory capacity limits the correctness of absolute judgments. Memory capacity is already well measured by other means, making redundant the informational analysis of absolute judgments. Originality/value – This paper presents a long-overdue comprehensive critical review of the established interpretation of absolute judgments in terms of “information transmitted”. An inevitable conclusion is reached: that published measurements of information transmitted actually measure memory capacity. A new, qualitative model is offered for the role of memory in absolute judgments. The model is well supported by recently revealed empirical properties of absolute judgments. (shrink)

Human biological memory systems have adapted to use technological artifacts to overcome some of the limitations of these systems. For example, when performing a difficult calculation, we use pen and paper to create and store external number symbols; when remembering our appointments, we use a calendar; when remembering what to buy, we use a shopping list. This chapter looks at the history of memory artifacts, describing the evolution from cave paintings to virtual reality. It first characterizes memory artifacts, memory systems, (...) and the two main functions such artifacts have, which are to aid individual users in completing memory tasks and as a cultural inheritance channel (section 2). It then outlines some of our first symbolic practices such as making cave paintings and figurines, and then moves on to outline several key developments in external representational systems and the artifacts that support these such as written language, numeral systems and counting devices, diagrams and maps, measuring devices, libraries and archives, photographs, analogue and digital computational artifacts, the World Wide Web, virtual reality, and smartphones (section 3). After that, it makes some brief points about the cumulative nature of the cultural evolution of memory artifacts and speculates about the possible future of memory artifacts, arguing that it is very difficult to look beyond an epistemological horizon of more than five years (section 4). (shrink)

Five experiments investigated the role of spatial connectedness between a pair of objects presented in the change detection task for the actual capacity of visual working memory (VWM) in healthy young adults (total N = 405). Three experiments yielded a surprising nonlinear relationship between the proportion of pair-wise connected objects and capacity, with the highest capacity observed for homogenous displays, when either all objects were connected or disjointed. A drop in capacity, ranging from an average of a quarter of an (...) object out of three objects maintained in VWM, was noted when only some objects were connected while others were disjointed. As indicated by another two experiments, this effect was specific to double-feature encoding, but disappeared when single visual features had to be memorized. No existing theoretical model of VWM can directly explain this novel effect. Overall, the nonlinear effect of spatial connectedness implies that representations in VWM possess hierarchical structure defined by wholes, parts, features, and their relations, and the heterogeneity of such a structure hinders VWM performance, while homogeneity facilitates it. (shrink)

This paper investigates some classical oppositional categories, like synthetic vs. analytic, posterior vs. prior, imagination vs. grammar, metaphor vs. hermeneutics, metaphysics vs. observation, innovation vs. routine, and image vs. sound, and the role they play in epistemology and philosophy of science. The epistemological framework of objective cognitive constructivism is of special interest in these investigations. Oppositional relations are formally represented using algebraic lattice structures like the cube and the hexagon of opposition, with applications in the contexts of modern color theory, (...) Kantian philosophy, Jungian psychology, and linguistics. (shrink)

It is often supposed one can draw a distinction, among the assumptions on which an inference rests, between certain background assumptions and certain more salient, or foregrounded, assumptions. Yet what may such a fore-v-background structure, or such structures, consist it? In particular, how do they relate to consciousness? According to a ‘Boring View’, such structures can be captured by specifying, for the various assumptions of the inference, whether they are phenomenally conscious, or access conscious, or else how easily available they (...) are to such consciousness. According to an ‘Interesting View’, there are fore-v-background structures over and above such classifications. The chapter gestures at reasons for thinking that an Interesting View at least merits exploration. The paper discusses some recent contributions to such a view in analytical philosophy; some remarks in Husserl on what he dubbed the horizonal dimension of acts of consciousness; and psychological work on the role of gist or schema representations in perception and memory. It is proposed that background assumptions can figure in consciousness by being as it were condensed into a consciously, though inattentively, entertained notion of their overall thematic gist, where this thematic gist gives the drift of a possible elucidation of how or why such-and-such salient grounds mean that so-and-so conclusion holds. (shrink)

We argue that the most ambitious version of the mental files theory of singular thought, according to which mental files are a wide-ranging psychological natural kind underlying all and only singular thinking, is unsupported by the available psychological data. Nevertheless, critical examination of the theory from a psychological perspective opens up promising avenues for research, especially concerning the relationship between our perceptual capacity to individuate and track basic individuals, and our higher level capacities for singular thought.

Eric Schwitzgebel (2011) argues that phenomenal judgments are in general less reliable than perceptual judgments. This paper distinguishes two versions of this unreliability thesis. The process unreliability thesis says that unreliability in phenomenal judgments is due to faulty domain-specific mechanisms involved in producing these judgments, whereas the statistical unreliability thesis says that it is simply a matter of higher numbers of errors. Against the process unreliability thesis, I argue that the main errors and limitations in making phenomenal judgments can be (...) accounted for by domain-general factors: attention, working memory limits and conceptualization. As these factors are shared with the production of perceptual judgments, errors in phenomenal judgments are not due to faulty domain-specific processes. Furthermore, this account defends phenomenal judgments against general scepticism by providing criteria for distinguishing between reliable and unreliable phenomenal judgments. (shrink)

This article presents theories of attention that attempt to derive their answer to the question of what attention is from their answers to the question of what it is for some activity to be done attentively. Such theories provide a distinctive account of the difficulties that are faced by the attempt to locate processes in the brain by which the phenomena of attention can be explained. Their account does not share the pessimism of theories suggesting that the concept of attention (...) is defective. Instead it reconstrues the explanatory relationship between attention and the processes that constitute it, in a way that is illustrated here by considering the relationship between attention and the processes that are identified by the biased competition theory. After considering some of the ways in which an adverbialist approach might be developed, the article concludes by suggesting some possible solutions to a problem concerning distraction, by which prominent adverbialist theories of attention have been dogged. (shrink)

In two experiments I examined what favorable conditions of early source monitoring performances are and what cognitive, social-cognitive and social factors are relevant to early source monitoring performances. Experiment 1 revealed that an action encoding mode is a favorable condition for 4- and 5-year-olds? external and reality monitoring performances but not for the 3-year-olds? source monitoring performances. Experiment 2 revealed that the familarity with the person source is a favorable condition for younger 3-, older 3-, 4- and 5-year old children. (...) The experiment also showed that multiple source attributions are possible at the middle of the third year of life and that the internal source monitoring instruction can be optimized for older but not for younger 3-year-old children. Both experiments revealed specific relations between the examined source monitoring performances and the selected working memory performances, verbal abilities, theory of mind abilities and social factors. (shrink)

Is attention both necessary and sufficient for consciousness? Call this central question of this treatise, “Q.” We commonly have the experience of consciously paying attention to something, but is it possible to be conscious of something you are not attending to, or to attend to something of which you are not conscious? Where might we find examples of these? This treatise is a quest to find an answer to Q in two parts. Part I reviews the foundations upon which the (...) discourse on Q is built. Different inputs to Q produce different answers. After consideration of the many ways “attention” and “consciousness” have been defined, I settle upon phenomenal consciousness and Executive Attention (defined as a suite of strategies for structuring cognition for further processing implemented by the executive of working memory) as the most interesting inputs to Q, and the ones on which Part II focuses. Attention without consciousness seems relatively easy to establish empirically, but consciousness without attention is much harder. The putative candidates all seem to have major problems, but I build a strong abductive case for the hitherto ignored case of foveal phenomenal overflow. We consciously see far more detail in our foveal fields than we can Executively Attend, although there is a serious obstacle to our ever confirming that empirically—identifying conscious content relies on Executive Attentional report. Triangulating the capacity limitations of attention, consciousness, and working memory strengthens this case for consciousness without attention, and suggests that cognition must work something like my “Witches’ Hat Model,” on which content can become conscious outside of Executive Attention or working memory. I conclude with some reflections on the implications of my arguments for the discourse on Q, and for other discourses such as the ontologies of attention and consciousness, theories of consciousness, some other cognitive concepts, and ethical considerations in humans, animals, and machines. A conclusive answer to Q continues to elude us. It may perhaps be an ultimately insoluble conundrum. But it is the very essence of humanity to seek an answer, and in so doing, to improve our understanding of our own nature: “The proper study of mankind is man.”1. (shrink)

Phrase structure trees have a hierarchical structure. In many subjects, most notably in {\bf taxonomy} such tree structures have been studied using ultrametrics. Here syntactical hierarchical phrase trees are subject to a similar analysis, which is much simpler as the branching structure is more readily discernible and switched. The occurrence of hierarchical structure elsewhere in linguistics is mentioned. The phrase tree can be represented by a matrix and the elements of the matrix can be represented by triangles. The height at (...) which branching occurs is not prescribed in previous syntactic models, but it is by using the ultrametric matrix. In other words the ultrametric approach gives a complete description of phrase trees, unlike previous approaches. The ambiguity of which branching height to choose, is resolved by postulating that branching occurs at the lowest height available. An ultrametric produces a measure of the complexity of sentences: presumably the complexity of sentences increases as a language is acquired so that this can be tested. All ultrametric triangles are equilateral or isosceles. Here it is shown that \={X} structure implies that there are no equilateral triangles. Restricting attention to simple syntax a minimum ultrametric distance between lexical categories is calculated. A matrix constructed from this ultrametric distance is shown to be different than the matrix obtained from features. It is shown that the definition of {\sc c-command} can be replaced by an equivalent ultrametric definition. The new definition invokes a minimum distance between nodes and this is more aesthetically satisfying than previous varieties of definitions. From the new definition of {\sc c-command} follows a new definition of of the central notion in syntax namely {\sc government}. (shrink)

This dissertation defends the reliability of first-person methods for studying consciousness, and applies first-person experiments to two philosophical problems: the experience of size and of the self. In chapter 1, I discuss the motivations for taking a first-person approach to consciousness, the background assumptions of the dissertation and some methodological preliminaries. In chapter 2, I address the claim that phenomenal judgements are far less reliable than perceptual judgements (Schwitzgebel, 2011). I argue that the main errors and limitations in making phenomenal (...) judgements are due to domain-general factors, which are shared in the formation of perceptual judgements. Phenomenal judgements may still be statistically less reliable than perceptual judgements, though I provide reasons for thinking that Schwitzgebel (2011) overstates the case for statistical unreliability. I also provide criteria for distinguishing between reliable and unreliable phenomenal judgements, hence defending phenomenal judgements against general introspective scepticism. Having identified the main errors in making phenomenal judgements, in chapter 3, I discuss how first-person experiments can be used to control for these errors. I provide examples, and discuss how they overcome attentional and conceptual errors, minimise biases, and exhibit high intersubjective reliability. In chapter 4, I investigate size experience. I use first-person experiments and empirical findings to argue that distant things looking smaller cannot be explained as an awareness of instantiated objective properties (visual angle or retinal image size). I also discuss how an awareness of uninstantiated objective properties cannot adequately account for the phenomenal character of size experience. This provides support for a subjectivist account of variance in size experience. In chapter 5, I investigate the sense of self. I distinguish between a weak sense of self (for-me-ness) and a strong sense of self in which there is a polarity between subject and object. I use first-person experiments from Douglas Harding to demonstrate an explicit strong sense of self, specifically when I point at where others see my face. I also argue that this sense of self is not explained by inference, thoughts, feelings, imagination nor the viewpoint. Rather, it is part of the structure of experience that I seem to be looking from here. Even if there is a sense of self, there may be no self. The question of chapter 6 is whether there can be a direct experience of the self. I argue that to function as a bearer of experience the subject must be single and lack sensory qualities in itself. I use Harding’s first-person experiments to investigate the visual gap where I cannot see my head. I argue that it conforms to the above criteria, and hence is a candidate for being the subject. This finding, in conjunction with the fact that I seem to be looking from the same location, provides prima facie evidence for the reality of the subject. I hold then that contrary to Hume and most philosophers since, that there can be a direct self-experience, if one knows which direction to attend. (shrink)

We show how an epistemology informed by cognitive science promises to shed light on an ancient problem in the philosophy of mathematics: the problem of exactness. The problem of exactness arises because geometrical knowledge is thought to concern perfect geometrical forms, whereas the embodiment of such forms in the natural world may be imperfect. There thus arises an apparent mismatch between mathematical concepts and physical reality. We propose that the problem can be solved by emphasizing the ways in which the (...) brain can transform and organize its perceptual intake. It is not necessary for a geometrical form to be perfectly instantiated in order for perception of such a form to be the basis of a geometrical concept. (shrink)

This paper aims to clarify the relationship between consciousness and attention through theoretical considerations about evolution. Specifically, we will argue that the empirical findings on attention and the basic considerations concerning the evolution of the different forms of attention demonstrate that consciousness and attention must be dissociated regardless of which definition of these terms one uses. To the best of our knowledge, no extant view on the relationship between consciousness and attention has this advantage. Because of this characteristic, this paper (...) presents a principled and neutral way to settle debates concerning the relationship between consciousness and attention, without falling into disputes about the meaning of these terms. A decisive conclusion of this approach is that extreme views on the relationship between consciousness and attention must be rejected, including identity and full dissociation views. There is an overlap between the two within conscious attention, but developing a full understanding of this mechanism requires further empirical investigations. (shrink)

Last year at VSS, Bullot, Droulez & Pylyshyn reported studies using a Modified Traveling Salesman Paradigm in which a virtual vehicle had to visit up to 10 targets once and only once, and in which the invisible targets were identified only by line segments pointing from the vehicle toward each target. We hypothesized that subjects used two distinct strategies: A “location-based strategy”, which kept track of where targets were located in screen coordinates, and a “segment-based strategy” that kept track of (...) which segments corresponded to visited targets. We report new studies that further explore these two strategies. Subjects passively observed a computer-controlled virtual vehicle that visited a number of targets. Two forms of display were used: an “Allocentric” display, in which the vehicle moved and the targets remained fixed in screen coordinates, and an “Egocentric” display, in which the vehicle's position on the screen remained fixed while the targets moved -- as if the environment were being viewed by an observer on the vehicle. At the end of each trial, the directional segments were extended to the edge of the screen and subjects were asked to perform two tasks by referring to these segments. In the “status task” observers had to indicate for each segment whether the corresponding target had been visited or not. In the “locating task” they had to locate each target along its directional segment. Performance on these two tasks measures the use of the two hypothesized strategies. Results showed that observers do well on the status task with 4 or 6 targets in both display conditions, but do poorly on the locating task, especially in the egocentric condition when there are more targets. These results are consistent with the hypothesis that in the egocentric condition the MTSP task is carried out primarily by segment-tracking, which can be viewed as a deictic strategy. (shrink)

What is Computational Intelligence (CI) and what are its relations with Artificial Intelligence (AI)? A brief survey of the scope of CI journals and books with ``computational intelligence'' in their title shows that at present it is an umbrella for three core technologies (neural, fuzzy and evolutionary), their applications, and selected fashionable pattern recognition methods. At present CI has no comprehensive foundations and is more a bag of tricks than a solid branch of science. The change of focus from methods (...) to challenging problems is advocated, with CI defined as a part of computer and engineering sciences devoted to solution of non-algoritmizable problems. In this view AI is a part of CI focused on problems related to higher cognitive functions, while the rest of the CI community works on problems related to perception and control, or lower cognitive functions. Grand challenges on both sides of this spectrum are addressed. (shrink)

The present empirical study investigates limitations of human visual working memory. The experiments of the present work involve the experimental paradigm of change detection using simple geometrical objects in the form of rectangles of different colour, length, and orientation. It can be shown, that a limited performance in the temporary storage of visual information has multiple sources. Limitations of VWM can be attributed to a limited capacity or a limited duration, but also to limitations in retrieval, which so far has (...) found only little attention. Key findings of the present study show, that a capacity limitation cannot be described by a simple and generally valid size of the store. It is in fact generally acknowledged that the capacity limitation of VWM is object-based, which means that the capacity can roughly be determined by the number of visual objects. However, it could be shown that the complexity of the objects has an influence on memory performance: Experimental evidence shows, e.g., that memory performance decreases, when an object is characterized not only by one feature, but by a number of features. The results are explained by increased storage demands for the binding of the features. Other key findings of the present study relate to the process of retrieval of information from VWM. For example, an asymmetric performance pattern could be observed: In a change detection task a memory performance was observed that corresponds to a capacity of 3 - 4 objects. In contrast a drastic decrease of performance corresponding to a capacity of only 1 object was observed, when the task was to find a matching item among changed distractors. These results lead to the idea of a change signal, by which the empirical data can be explained. The change signal is elicited by a local mismatch between the information stored in VSTM and perceptual online information. The retrieval process is efficient, when the change signal can be used in the memory task. However, retrieval is extremely limited, when in the presence of multiple changes a less efficient strategy has to be applied. In the course of the present study, moreover, it became evident that there are various links between VWM processes and visual attention. Visual attention is probably crucial for feature binding in VWM. In retrieval the change signal probably involves mechanisms of visual attention. The present study could, therefore, contribute to a clarification of the relation between VWM and visual attention. (shrink)

Recent studies of non-conscious processing have indicated that visually processed non-conscious informationcan be used to influence behaviour after as much as 5000 ms. This study further explores the possibilities of nonconsciousvisual working memory retention. Twelve participants were in this study instructed to memorizemasked faces and then make decisions based on what they believe they saw or guess intuitively. Results indicatethat increased working memory load only affected conscious trials, suggesting non-conscious stimulus remainedunperceived. Since no consciousness effect was observed when measuring response (...) times of congruent trials thisstudy do not support non-conscious working memory retention. (shrink)

External representations play a crucial role in learning. At the same time, cognitive load theory suggests that the possibility of learning depends on limited resources of the working memory and on cognitive load imposed by instructional design and representation tools. Both these observations motivate a critical look at Computer-Supported Argument Visualization tools that are supposed to facilitate learning. This paper uses cognitive load theory to compare the cognitive efficacy of RationaleTM 2 and AGORA.

Argues for a failure of correspondence between perceptual representation and what it is like to perceive. If what it is like to perceive is grounded in perceptual representation, then, using considerations of veridical representation, we can show that inattentive peripheral perception is less representationally precise than attentive foveal perception. However, there is empirical evidence to the contrary. The conclusion is that perceptual representation cannot ground what it is like to perceive.

Multitasking behavior and working memory training are important topics in psychological science. The present thesis systematically investigated the underlying cognitive constructs of multitasking behavior and the cognitive strategies related to transfer effects of working memory training, which were described in two empirical studies. In the first study, we examined the underlying cognitive constructs associated with the concept of multitasking behavior. Although prior investigations have revealed cognitive abilities to be important predictors of multitasking behavior, few studies have been conducted on the (...) relation between executive functions and multitasking behavior. In this regard, the current investigation explored the importance of EFs, working memory capacity, relational integration, and divided attention to multitasking behavior. A sample of 202 young adults completed a battery of EFs, three WMC tests, three relational integration tests, two divided attention tests, and a multitasking scenario. Our study provided several key findings. First, in direct replication attempts, we could replicate the multitasking behavior model and partially replicate the three-factor and nested factors EFs models. Second, the regression analyses revealed that updating, inhibition, relational integration, and divided attention had strong contributions in explaining multitasking behavior variance, whereas shifting and WMC did not show any explanatory power beyond these constructs. Finally, using structural equation modeling, we found that the general EF ability representing variance common to shifting, updating, and inhibition highly overlapped with multitasking behavior. Our results are of value not only to shed light on the relevant cognitive correlates of multitasking behavior but also to position multitasking behavior in an established framework of cognitive abilities. Additionally, by providing strong empirical evidence in favor of cognitive constructs of multitasking behavior, this study builds the necessary groundwork for steering future research to elucidate the etiology of underlying relations between these specific cognitive correlates and multitasking behavior. The second study inspected how transfer occurs on material-specific tasks, rather than other task types within the working memory training framework. Despite numerous attempts of using training interventions to increase WMC, the role of cognitive strategy in explaining the transfer effects is not yet experimentally investigated. We hypothesized that transfer would occur when a similar cognitive strategy is applied in solving both the trained and transfer tasks. According to this idea, we examined the strategic approach by directly using tasks that allow for specific strategies and tasks that do not. In particular, training with verbal and numerical materials should show transfer to figural material, and the other way around. Additionally, differences between visual and verbal cognitive strategies could lead to differential transfer effects on working memory tasks. Eighty young adults received training on two working memory operations: storage and processing, and relational integration with four different materials verbal/numerical/figural /figural, and another 17 served as active control group and 8 as passive group. Before and after 12 days of adaptive training, performance on the storage and processing, and on the relational integration tasks was assessed. Linear-mixed effects modeling revealed four important findings. First, following training, there were reliable improvements on the performance of trained storage and processing, and relational integration tasks, compared to the active control group. However, such training did not generalize to measures of the same working memory operation with different materials in most cases. Second, the only transfer effect was observed between numerical and figural material within relational integration tasks, thereby confirming our hypothesis. Third, no transfer was detected between storage and processing, and relational integration. Finally, there was no direct evidence supporting the influence of cognitive strategies on transfer effects. Together, the present findings provide strong evidence for growing theories of multitasking behavior and working memory training, emphasizing the importance of cognitive underpinnings of multitasking behavior and specifying the efficacy of working memory intervention only on material-specific tasks, which may be emerged from the acquisition of task-specific cognitive strategies. Although the current investigation did not yet provide clear evidence about the strategic approach, the combination of material-specific mechanisms with a general boost in the underlying cognitive strategies provides an important and interesting perspective for future work. (shrink)

In the following sections, English summaries of the three studies presented in this dissertation are given. For a detailed German synopsis of the present work, see chapter 8. Research in the field of aging and dementia is a main concern as the population of elderly people is growing continuously due to increasing life expectancy and thus, an accumulative number of people who live well beyond 65 years of age run a risk of developing age-associated neurodegenerative disorders of cognitive function, such (...) as Alzheimer’s disease, emerging as a major health problem. The present work is based on growing evidence that deficits in visual selective attention occur early in the progression to AD and therefore might be present as the first non-memory deficits at the early prodromal stage of mild cognitive impairment. The present dissertation was performed to contribute to the still ongoing debate as to whether certain aspects of visual selective attention are par-ticularly vulnerable or preserved, especially at the stage of MCI, and whether attentional func-tioning might be qualitatively and/ or quantitatively different from attentional performance at the AD stage on the one hand or normal functioning on the other hand. As theoretical basis, Bundesen’s theory of visual attention was employed to assess several latent, mathematically independent and quantitative parameter es-timates which are derived from two highly comparable paradigms – computerized whole re-port and partial report of briefly presented visual letter arrays. Central conclusions arising out of TVA-based investigations point at four central strengths of this tool for attentional assessment – the quality criteria sensitivity, specificity, reliability and validity. Study 1: In AD, the amyloid cascade hypothesis assumes that rising plaque and tangle burden invokes loss of nerve cells through direct and indirect effects on synaptic, neuronal and neuritic function, resulting in progressive intellectual decline. Thus, sensitive biomarkers loading functionally on the neural alterations invoked by AD from early on, might improve the possibility to identify at risk subjects in time, providing a chance for effective treatment. The first study examined whether cognitive parameters for estimating the capacity of visual attention might serve that purpose. Based on Bundesen’s TVA, visual information uptake was analyzed in 18 subjects with probable AD, 18 subjects with amnestic MCI, and 18 healthy elderly control subjects. Groups were matched for gender, age, and education. From a whole report task requiring ver-bal report of briefly presented letters, four parameters were derived, characterizing different aspects of visual processing capacity: perceptual threshold t0, iconic memory μ, processing speed C, and visual short-term memory storage capacity K. Comparison of these attentional parameters between groups revealed an elevation of the per-ceptual threshold already in MCI subjects, while processing speed and VSTM storage capacity showed a significant decline for AD patients, only. AD patients on medication with acetyl-choline esterase inhibitors had higher processing speed, but were still below the level of MCI patients. Perceptual threshold values were significantly correlated with disease duration, but not with cognitive measures. Conversely, speed and VSTM were significantly related to cog-nitive scores, but not to disease duration. In particular, VSTM storage was related to neurop-sychological tasks applying visual material, while speed showed an additional relationship also to measures of verbal memory. These results indicate a staged pattern of deficits affecting pre-attentive visual processing in MCI, and attentive processing in AD. They fit into the amyloid cascade hypothesis according to which the neuropathology of AD is characterized by a net accumulation and deposition of β-amyloid in the initial phase, giving rise to neuronal and neuritic dysfunction. Later, gradual neuronal loss and transmitter disturbances finally cause the increasing intellectual de-cline during further progression of the disease. A threshold elevation may thus be considered as a possible index of impaired neuronal functioning prior to cell death, while speed and VSTM deficits may be indicative already of a substantial loss of neuronal cell assemblies and a degeneration of neurotransmitter systems. Study 2: AD is the most frequent form of dementia which appears both as a familial and a sporadic va-riant. In the by far more frequent sporadic form, a genetic risk factor is also implicated, in that carriers of the apolipoprotein E ε4 allele have a 3 to 15 times higher risk of develop-ing the disease, compared to non-carriers. Using an identical TVA-based partial report paradigm as in the present study, Finke et al. had found a close relationship between the severity of the underlying genetic pathology in another neurodegenerative, namely Huntington’s, disease and the direction and degree of spatial attentional weighting. Sensitive tools for assessing selective visual attention might serve as early cognitive markers in the course of AD and therefore enhance the identification rate of at-risk subjects at the MCI stage as well as of subjects with underlying genetic risk. The second study aimed at examining whether attentional parameters of visuospatial and task-related selection are appropriate means for that purpose. Visual selective attention was investigated in 32 patients with amnestic MCI, 16 patients with probable AD, and 36 healthy elderly control subjects. Groups were matched for age, gender and educational level. In combination with Bundesen’s TVA, two mathematically in-dependent and quantitative parameter estimates were derived from a partial report of briefly presented letter arrays: top-down control of attentional selection, representing task-related at-tentional weighting for prioritizing relevant visual objects, and spatial distribution of atten-tional weights across the left and right visual hemifield. Compared to controls, MCI patients showed significantly reduced top-down controlled selec-tion which further deteriorated in AD subjects. Moreover, attentional weighting was signifi-cantly unbalanced across hemifields in MCI and tended to be more lateralized in AD. The ma-jority of patients was biased to the left. Across MCI and AD patients, ApoE4 carriers revealed a leftward spatial bias. The leftward bias was the more pronounced the younger the ApoE4-positive patients and the earlier disease onset. ApoE4-negative subjects showed balanced attentional weighting. These results indicate that impaired top-down control may be linked to early dysfunction of cortico-cortical networks connecting parietal and frontal lobes. Accompanying, an early inter-hemispheric asymmetry in temporo-parietal cortical interactions might cause a pathological spatial bias. As the inheritance of ApoE4 is associated with an interhemispheric imbalance in parietal cortical interactions, a pathological spatial bias may function as early cognitive marker for detecting subjects at risk for probable AD. Study 3: In the latter study, the TVA-based partial report paradigm proved to be a sensitive tool for ve-rifying that both, deficits in task-related selection and a pathological attentional imbalance, are already present at the early stage of amnestic MCI and increase further at the AD stage. It was hypothesized that these deficiencies in selective attention may result from an early disconnection syndrome and an interhemispheric imbalance in cortical interactions, respectively, in the fronto-parietal attention network, before gradual neuronal loss leads to further decline in selective attentional and intellectual functions at later stages. In the third study, these hypotheses were tested by investigat-ing the relationship of both partial report parameters, top-down control α and especially the laterality index of attentional weighting wλ, to regional glucose metabolism measured by rest-ing-state positron emission tomography in a sample of 30 amnestic MCI or mild AD patients. Hypometabolism across all patients was slightly increased in the left hemisphere. Interestingly, the more reduced the metabolism in the left temporo-parietal junction the more pro-nounced was the top-down control deficit. Accordingly, hypometabolism in the left TPJ pre-dicted the magnitude of the spatial bias. Furthermore, relative hypometabolism in the left TPJ and left inferior parietal lobe as compared to the right TPJ and right IPL, respectively, was correlated with direction and degree of spatial bias. Taken together, PET imaging results support the hypotheses that, one the one hand, early def-icits in task-related weighting may result from a fronto-parietal disconnection syndrome al-ready at the stage of MCI. On the other hand, very early AD seems to be also associated with an interhemispheric imbalance of metabolism, particularly in the temporo-parietal cortices, resulting in a correspondingly directed and distinctive visuo-spatial attentional bias. Conclusions and outlook: This dissertation intended to investigate the probable valuable contribution of the whole and partial report of briefly presented letter arrays based on Bundesen’s theory of visual attention in assessing am-nestic MCI and AD patients in comparison to healthy elderly control subjects. The results of the three presented studies suggest a staging model of visual selective atten-tional impairments in MCI and AD. Deficits of pre-attentive processing, task-related and spatial weighting were already detectable in MCI patients, while aspects of processing capacity were still intact. At a later stage of the disease, further deterioration of top-down control α and increasing lateralization of spatial weighting wλ accompanied impairments in perceptual processing speed C and VSTM storage capacity K. In conclusion, the TVA-based assessment of selective visual attention proved to be a sensitive diagnostic tool for revealing subtle deficits already at the stage of MCI which might exhibit the capability of an early cognitive marker for the identification of subjects at risk of AD. To address this question, this survey needs to be complemented by longitudinal studies. (shrink)

Conscious experience is the direct observation of conscious events. Human conscious experience is four-dimensional. Conscious events are linked (associated) by spacetime intervals to produce a coherent conscious experience. This explains why conscious experience appears to us the way it does. Conscious experience is an orientation in space and time, an understanding of the position of the observer in space and time. Causality, past-future relations, learning, memory, cognitive processing, and goal-directed actions all evolve from four-dimensional conscious experience. A neural correlate for (...) four-dimensional conscious experience can be found in the human brain and is modelled by Einstein's special theory of relativity. The relativistic concept of spacetime interval is central for understanding conscious experience and cognition. (shrink)

Theories of consciousness divide over whether perceptual consciousness is rich or sparse in specific representational content and whether it requires cognitive access. These two issues are often treated in tandem because of a shared assumption that the representational capacity of cognitive access is fairly limited. Recent research on working memory challenges this shared assumption. This paper argues that abandoning the assumption undermines post-cue-based “overflow” arguments, according to which perceptual conscious is rich and does not require cognitive access. Abandoning it also (...) dissociates the rich/sparse debate from the access question. The paper then explores attempts to reformulate overflow theses in ways that don’t require the assumption of limited capacity. Finally, it discusses the problem of relating seemingly non-probabilistic perceptual consciousness to the probabilistic representations posited by the models that challenge conceptions of cognitive access as capacity-limited. (shrink)

Previous studies have suggested that visual short-term memory (VSTM) has a storage limit of approximately four items. However, the type of high-threshold (HT) model used to derive this estimate is based on a number of assumptions that have been criticized in other experimental paradigms (e.g., visual search). Here we report findings from nine experiments in which VSTM for color, spatial frequency, and orientation was modeled using a signal detection theory (SDT) approach. In Experiments 1-6, two arrays composed of multiple stimulus (...) elements were presented for 100 ms with a 1500 ms ISI. Observers were asked to report in a yes/no fashion whether there was any difference between the first and second arrays, and to rate their confidence in their response on a 1-4 scale. In Experiments 1-3, only one stimulus element difference could occur (_T_ = 1) while set size was varied. In Experiments 4-6, set size was fixed while the number of stimuli that might change was varied (_T_ = 1, 2, 3, and 4). Three general models were tested against the receiver operating characteristics generated by the six experiments. In addition to the HT model, two SDT models were tried: one assuming summation of signals prior to a decision, the other using a max rule. In Experiments 7-9, observers were asked to directly report the relevant feature attribute of a stimulus presented 1500 ms previously, from an array of varying set size. Overall, the results suggest that observers encode stimuli independently and in parallel, and that performance is limited by internal noise, which is a function of set size. (shrink)

Using a novel enumeration task, we examined the encoding of spatial information during subitizing. Observers were shown masked presentations of randomly-placed discs on a screen and were required to mark the perceived locations of these discs on a subsequent blank screen. This provided a measure of recall for object locations and an indirect measure of display numerosity. Observers were tested on three stimulus durations and eight numerosities. Enumeration performance was high for displays containing up to six discs—a higher subitizing range (...) than reported in previous studies. Error in the location data was measured as the distance between corresponding stimulus and response discs. Overall, location errors increased in magnitude with larger numerosities and shorter display durations. When errors were computed as disc distance from display centroid, results suggest a compressed representation by observers. Additionally, enumeration and localization accuracy increased with display regularity. (shrink)