How can we explain our capacity to think about particulars in our external environment? Many philosophers have answered this question in terms of a sophisticated conception of space and time and the movement of objects therein. A more recent reaction against this view sought to explain this capacity solely in terms of perceptual mechanisms of object individuation. Neither explanation remains fully satisfactory. This book argues for a more desirable middle ground in terms of a pragmatist approach to demonstrative thought, where (...) this capacity is explained through graded practical knowledge of objects. This view allows us to do justice to important insights put forward by both positions criticized in the book, while avoiding their potential shortcomings. It also paves the way to a more pragmatist approach to the theory of mental representation, where the notion of practical knowledge is allowed to play a central role in our cognitive life. Finally, it shows how practical knowledge may be firmly rooted in neurobiological processes and mechanisms that conform to what the empirical sciences tell us about the mind. (shrink)

The book presents the case that cognitive science should turn its attention to developing theories of human cognition that cover the full range of human perceptual, cognitive, and action phenomena. Cognitive science has now produced a massive number of high-quality regularities with many microtheories that reveal important mechanisms. The need for integration is pressing and will continue to increase. Equally important, cognitive science now has the theoretical concepts and tools to support serious attempts at unified theories. The argument is made (...) entirely by presenting an exemplar unified theory of cognition both to show what a real unified theory would be like and to provide convincing evidence that such theories are feasible. The exemplar is SOAR, a cognitive architecture, which is realized as a software system. After a detailed discussion of the architecture and its properties, with its relation to the constraints on cognition in the real world and to existing ideas in cognitive science, SOAR is used as theory for a wide range of cognitive phenomena: immediate responses ; discrete motor skills ; memory and learning ; problem solving ; language ; and development. The treatments vary in depth and adequacy, but they clearly reveal a single, highly specific, operational theory that works over the entire range of human cognition, SOAR is presented as an exemplar unified theory, not as the sole candidate. Cognitive science is not ready yet for a single theory – there must be multiple attempts. But cognitive science must begin to work toward such unified theories. (shrink)

Two experiments examined false recall for lists of semantically and phonologically associated words as a function of presentation duration. Veridical recall increased with long exposure durations for all lists. For semantically associated lists, false recall increased from 20–250 ms, then decreased. There was a high level of false recall with 20 ms durations for phonologically associated lists , which declined as duration increased. In Experiment 2, for lists presented at 20 and 50 ms rates, false recall given zero correct recall (...) was observed frequently, suggesting that conscious recollection of studied words was not necessary for phonological false memory. Differences between phonologically and semantically associated lists were consistent with a feature integration model based on automatic initial processing of phonetic features of words. (shrink)

We show that early vision can use monocular cues to rapidly complete partially-occluded objects. Visual search for easily detected fragments becomes difficult when the completed shape is similar to others in the display; conversely, search for fragments that are difficult to detect becomes easy when the completed shape is distinctive. Results indicate that completion occurs via the occlusion-triggered removal of occlusion edges and linking of associated regions. We fail to find evidence for a visible filling-in of contours or surfaces, but (...) do find evidence for a "functional" filling-in that prevents the constituent fragments from being rapidly accessed. As such, it is only the completed structures—and not the fragments themselves—that serve as the basis for rapid recognition. (shrink)

In the critical trial of the "inattention paradigm" about 25% of the participants did not notice the target stimulus. A significant percent of these "inattentionally blind" subjects did not detect the target objects when explicitly asked about them. Nevertheless, in an implicit test these subjects showed that the target objects were processed. The "inattentionally blind" subjects in the inattention paradigm are blind to the critical stimulus in the same sense that subjects in the Stroop task are blind to the meaning (...) of the presented words. In both cases blindness reflects the limitations of the representations resulting from automatic processing. Therefore, these results are best conceptualized as indicating automatic processing of unattended stimuli. (shrink)

We show that cast shadows can have a significant influence on the speed of visual search. In particular, we find that search based on the shape of a region is affected when the region is darker than the background and corresponds to a shadow formed by lighting from above. Results support the proposal that an early-level system rapidly identifies regions as shadows and then discounts them, making their shapes more difficult to access. Several constraints used by this system are mapped (...) out, including constraints on the luminance and texture of the shadow region, and on the nature of the item casting the shadow. Among other things, this system is found to distinguish between line elements (items containing only edges) and surface elements (items containing visible surfaces), with only the latter deemed capable of casting a shadow. (shrink)

East Asians and Westerners differ in various aspects of perception and cognition. For example, visual memory for East Asians is believed to be more influenced by the contextual aspects of a scene than is the case for Westerners (Masuda & Nisbett, 2001). There are also differences in visual search: for Westerners, search for a long line among short is faster than for short among long, whereas this difference does not appear to hold for East Asians (Ueda et al., submitted). However, (...) it is unclear how these group-level differences originate. To investigate the extent to which they depend upon environment, we tested visual search and visual memory in East Asian immigrants who had lived in Canada for different amounts of time. Recent immigrants were found to exhibit no search asymmetry, unlike Westerners who had spent their lives in Canada. However, immigrants who had lived in Canada for more than two years showed performance comparable to that of Westerners. These differences could not be explained by the general analytic/holistic processing distinction believed to differentiate Westerners and East Asians, since all observers showed a strong holistic tendency for visual recognition. Results instead support the suggestion that exposure to a new environment can significantly affect the particular processes used to perceive a given stimulus. (shrink)

A set of visual search experiments tested the proposal that focused attention is needed to detect change. Displays were arrays of rectangles, with the target being the item that continually changed its orientation or contrast polarity. Five aspects of performance were examined: linearity of response, processing time, capacity, selectivity, and memory trace. Detection of change was found to be a self-terminating process requiring a time that increased linearly with the number of items in the display. Capacity for orientation was found (...) to be about 5 items, a value comparable to estimates of attentional capacity. Observers were able to filter out both static and dynamic variations in irrelevant properties. Analysis also indicated a memory for previously-attended locations. These results support the hypothesis that the process needed to detect change is much the same as the attentional process needed to detect complex static patterns. Interestingly, the features of orientation and polarity were found to be handled in somewhat different ways. Taken together, these results not only provide evidence that focused attention is needed to see change, but also show that change detection itself can provide new insights into the nature of attentional processing. (shrink)

This paper discusses several key issues concerning consciousness and human vision. A brief overview is presented of recent developments in this area, including issues that have been resolved and issues that remain unsettled. Based on this, three Hilbert questions are proposed. These involve three related sets of issues: the kinds of visual experience that exist, the kinds of visual attention that exist, and the ways that these relate to each other.

This paper explores the ways in which resource limitations influence the nature of perceptual and cognitive processes. A framework is developed that allows early visual processing to be analyzed in terms of these limitations. In this approach, there is no one ``best'' system for any visual process. Rather, a spectrum of systems exists, differing in the particular trade-offs made between performance and resource requirements.

Large changes in a scene often become difficult to notice if made during an eye movement, image flicker, movie cut, or other such disturbance. It is argued here that this _change blindness_ can serve as a useful tool to explore various aspects of vision. This argument centers around the proposal that focused attention is needed for the explicit perception of change. Given this, the study of change perception can provide a useful way to determine the nature of visual attention, and (...) to cast new light on the way that it is?and is not?involved in visual perception. To illustrate the power of this approach, this paper surveys its use in exploring three different aspects of vision. The first concerns the general nature of _seeing_. To explain why change blindness can be easily induced in experiments but apparently not in everyday life, it is proposed that perception involves a _virtual representation_, where object representations do not accumulate, but are formed as needed. An architecture containing both attentional and nonattentional streams is proposed as a way to implement this scheme. The second aspect concerns the ability of observers to detect change even when they have no visual experience of it. This _sensing_ is found to take on at least two forms: detection without visual experience (but still with conscious awareness), and detection without any awareness at all. It is proposed that these are both due to the operation of a nonattentional visual stream. The final aspect considered is the nature of visual attention itself?the mechanisms involved when _scrutinizing_ items. Experiments using controlled stimuli show the existence of various limits on visual search for change. It is shown that these limits provide a powerful means to map out the attentional mechanisms involved. (shrink)

In the not-too-distant past, vision was often said to involve three levels of processing: a low level concerned with descriptions of the geometric and photometric properties of the image, a high level concerned with abstract knowledge of the physical and semantic properties of the world, and a middle level concerned with anything not handled by the other two. The negative definition of mid-level vision contained in this description reflected a rather large gap in our understanding of visual processing: How could (...) the here-and-now descriptions of the low levels combine with the enduring knowledge of the high levels to produce our perception of the surrounding world? A number of experimental and theoretical efforts have been made over the past few decades to solve this "mid-level crisis". One of the more recent of these is based on the phenomenon of change blindness—the difficulty in seeing a large change in a scene when the transients accompanying that change no longer convey information about its location (Rensink, O'Regan, & Clark, 1997; Rensink, 2000a). Phenomenologically, this effect is quite striking: the change typically is not seen for several seconds, after which it suddenly snaps into awareness. During the time the change remains "invisible", there is an apparent disconnection of the low-level descriptions (which respond to the change) from subjective visual experience (which does not). As such, this effect would seem to have the potential to help us understand how mid-level mechanisms might knit low- and high-level processes into a coherent representation of our surroundings. -/- It is argued here that this potential can indeed be realized, and that change blindness can teach us much about the nature of mid-level vision.3 A number of studies are first reviewed showing that the perception of a scene does not involve a steady buildup of detailed representation: rather, it is a dynamic process, with focused attention playing one of the main roles, viz., forming coherent object representations whenever needed. It is then argued that change blindness can also shed considerable light on the nature of focused attention itself, such as its speed, capacity, selectivity, and ability to bind together visual properties into coherent structures. (shrink)

A compositional theory of perceptual representations would explain how the accuracy conditions of a given type of perceptual state depend on the contents of constituent perceptual representations and the way those constituents are structurally related. Such a theory would offer a basic framework for understanding the nature, grounds, and epistemic significance of perception. But an adequate semantics of perceptual representations must accommodate the holistic nature of perception. In particular, perception is replete with context effects, in which the way one perceptually (...) represents one aspect of a scene (including the position, size, orientation, shape, color, motion, or even unity of an object) normally depends on how one represents many other aspects of the scene. The ability of existing accounts of the semantics of perception to analyze context effects is at best unclear. Context effects have even been thought to call into question the very feasibility of a systematic semantics of perception. After outlining a compositional semantics for a rudimentary set of percepts, I draw on empirical models from perceptual psychology to show how such a theory must be modified to analyze context effects. Context effects arise from substantive constraints on how perceptual representations can combine and from the different semantic roles that perceptual representations can have. I suggest that context effects are closely tied to the objectivity of perception. They arise from a perceptual grammar that functions to facilitate the composition of reliably accurate representations in an uncertain but structured world. (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)

The present study explored the concept of cognitive reserve by using a testing-the-limits paradigm. 140 young and 140 older adults were provided with extensive retest practice in the Digit Symbol Substitution Test and a visual search task. Cognitive abilities and personality dimensions served as predictors of retest improvement. Latent Growth Curve analyses demonstrated greater DSST improvement for the young group, but similar visual search improvement for both age groups, indicating age-independent cognitive reserve in visual search. Improvement rates for both tasks (...) were weakly correlated, speaking rather for task-specific learning than for a general cognitive reserve. Cognitive reserve was rather independent from cognitive abilities and, with one exception, also from personality dimensions. Implications for cognitive reserve in general and DSST and visual search retest learning in particular are discussed. (shrink)

In the visual search paradigm, participants’ task is to detect the presence or absence of a target item, which is presented in an array of distractor items. Usually it is found that performance is dependent on specific properties of the visual display, for example, the number of items to be searched or the similarity between display items. However, recent research has demonstrated that memory mechanisms can also affect search behaviour. Further, it was found that memory mechanisms can, in principle, be (...) either facilitatory or inhibitory, that is, that the processing of the item locations, features, or search objects themselves can be improved or impeded, respectively. This thesis investigated the effects of facilitatory and inhibitory memory mechanisms based on the element positions within the search display; facilitatory memory mechanisms based on the features of the search elements; and inhibitory memory mechanisms based on the search objects themselves. (shrink)