Traditionally it is taken for granted that mental imagery (MI) is a mental representation (MR) of some kind or format. This yields that theory of MR can give an adequate and exhaustive explanation of MI. Such co-relation between the two is usually seen as unproblematic. But is it really so? This article aims at challenging the theoretical claim that the dominant ‘two-world’ account of MR can adequately explain MI. Contrary to the standard theory of MR, there are reasons to believe (...) that: (a) MI has different cognitive architecture, (b) the relations between elements of MI are dynamic, (c) relations between elements of MI are context-dependent. Consequently, it follows that dominant account of MR neglects important characteristics of MI and, thus, fails to give a comprehensive explanation of the latter. Alternatively, I will argue that a sign-theoretic approach, proposed by C. S. Peirce, can suggest a promising explanation of MI and fully account for the divergent empirical data on the matter. (shrink)

A leading theoretical framework for naturalistic explanation of mind holds that we explain the mind by positing progressively "stupider" capacities ("homunculi") until the mind is "discharged" by means of capacities that are not intelligent at all. The so-called homuncular fallacy involves violating this procedure by positing the same capacities at subpersonal levels. I argue that the homuncular fallacy is not a fallacy, and that modern-day homunculi are idle posits. I propose an alternative view of what naturalism requires that reflects how (...) the cognitive sciences are actually integrating mind and matter. (shrink)

Artificial Intelligence is at a turning point, with a substantial increase in projects aiming to implement sophisticated forms of human intelligence in machines. This research attempts to model specific forms of intelligence through brute-force search heuristics and also reproduce features of human perception and cognition, including emotions. Such goals have implications for artificial consciousness, with some arguing that it will be achievable once we overcome short-term engineering challenges. We believe, however, that phenomenal consciousness cannot be implemented in machines. This becomes (...) clear when considering emotions and examining the dissociation between consciousness and attention in humans. While we may be able to program ethical behavior based on rules and machine learning, we will never be able to reproduce emotions or empathy by programming such control systems—these will be merely simulations. Arguments in favor of this claim include considerations about evolution, the neuropsychological aspects of emotions, and the dissociation between attention and consciousness found in humans. Ultimately, we are far from achieving artificial consciousness. (shrink)

According to the two visual systems model, the visual processing of objects divides into semantic and pragmatic processing. We provide various criteria for this distinction. Further, we argue that both the semantic and pragmatic processing of visual information about objects should be divided into low-level processing and high-level processing. Finally, we re-evaluate the contribution of the human parietal lobe to the concious visual perception of spatial relations among objects.

Research in vision science, developmental psychology, and the foundations of cognitive science has led some theorists to posit referential mechanisms similar to indices. This hypothesis has been framed within a Fodorian conception of the early vision module. The article shows that this conception is mistaken, for it cannot handle the ‘interface problem’—roughly, how indexing mechanisms relate to higher cognition and conceptual thought. As a result, I reject the inaccessibility of early vision to higher cognition and make some constructive remarks on (...) the perception–cognition interface. -/- 1 The Case for Visual Indices 1.1 Preliminary assumptions 1.2 Transcendental arguments 1.3 Evidence from vision science 2 Visual Indices, Object Files, and Fodorian Modularity 3 The Interface Problem 3.1 Top-down attention and modularity 3.2 Selective attention and information 4 Revising the Indexing Hypothesis 4.1 Revising the perception–cognition interface 4.2 Revising the modularity of early vision 5 Concluding Remarks. (shrink)

I show how a conversational process that takes simple, intuitively meaningful steps may be understood as a sophisticated computation that derives the richly detailed, complex representations implicit in our knowledge of language. To develop the account, I argue that natural language is structured in a way that lets us formalize grammatical knowledge precisely in terms of rich primitives of interpretation. Primitives of interpretation can be correctly viewed intentionally, as explanations of our choices of linguistic actions; the model therefore fits our (...) intuitions about meaning in conversation. Nevertheless, interpretations for complex utterances can be built from these primitives by simple operations of grammatical derivation. In bridging analyses of meaning at semantic and symbol‐processing levels, this account underscores the fundamental place for computation in the cognitive science of language use. (shrink)

On a traditional or default view of the grasping or understanding of a singular proposition by an individual, it is assumed to be a unitary or holistic activity. However, naturalistic views of cognition plausibly could analyze propositional thinking in terms of more than one distinctive functional stage of cognitive processing, suggesting at least the potential legitimacy of a non-unitary analysis of propositional grasping. We outline a novel dual-component view of this kind, and show that it is well supported by current (...) cognitive science research. (shrink)

In this paper, I claim that extant empirical data do not support a radically embodied understanding of the mind but, instead, suggest (along with a variety of other results) a massively representational view. According to this massively representational view, the brain is rife with representations that possess overlapping and redundant content, and many of these represent other mental representations or derive their content from them. Moreover, many behavioral phenomena associated with attention and consciousness are best explained by the coordinated activity (...) of units with redundant content. I finish by arguing that this massively representational picture challenges the reliability of a priori theorizing about consciousness. (shrink)

��In four experiments we address the question whether several visual objects can be selected voluntarily (exogenously) and then tracked in a Multiple Object Tracking paradigm and, if so, whether the selection involves a different process. Experiment 1 showed that items can indeed be selected based on their labels. Experiment 2 showed that to select the complement set to a set that is automatically (exogenously) selected — e.g. to select all objects not flashed — observers require additional time and that given (...) 1080 ms they were able to select and track them as well as those selected automatically. Experiment 3 showed that the additional time needed in the previous experiment cannot be attributed solely to time required to disengage attention from the initially automatic selections. Experiment 4 showed that the added time provides a monotonically greater benefit when there are more targets, suggesting a serial process. These results are discussed in relation to the Visual Index (FINST) theory which assumes that visual indexes are captured by a data-driven process. It is suggested that voluntarily allocated attention can be used to facilitate the automatic attention capture by objects of interest. (shrink)

I shall propose five theses on de re states and attitudes. To be a de re state or attitude is to bear a peculiarly direct epistemic and representational relation to a particular referent in perception or thought. I will not dress this bare statement here. The fifth thesis tries to be less coarse. The first four explicate and restrict context- bound, singular, empirical representation, which constitutes a significant and central type of de re state or attitude.

In the past decade there has been renewed interest in the study of mental imagery. Emboldened by new findings from neuroscience, many people have revived the idea that mental imagery involves a special format of thought, one that is pictorial in nature. But the evidence and the arguments that exposed deep conceptual and empirical problems in the picture theory over the past 300 years have not gone away. I argue that the new evidence from neural imaging and clinical neuropsychology does (...) little to justify this recidivism because it does not address the format of mental images. I also discuss some reasons why the picture theory is so resistant to counterarguments and suggest ways in which non-pictorial theories might account for the apparent spatial nature of images. (shrink)

This paper contrasts three different schemes of reference relevant to understanding systems of perceptual representation: a location-based system dubbed "feature-placing", a system of "visual indices" referring to things called "proto-objects", and the full sortal-based individuation allowed by a natural language. The first three sections summarize some of the key arguments (in Clark, 2000) to the effect that the early, parallel, and pre-attentive registration of sensory features itself constitutes a simple system of nonconceptual mental representation. In particular, feature integration--perceiving something as (...) being both F and G, where F and G are sensible properties registered in distinct parallel streams--requires a referential apparatus. Section V. reviews some grounds for thinking that at these earliest levels this apparatus is location-based: that it has a direct and nonconceptual means of picking out places. Feature-placing is contrasted with a somewhat more sophisticated system that can identify and track four or five "perceptual objects" or "proto-objects", independently of their location, for as long as they remain perceptible. Such a system is found in Zenon Pylyshyn's fascinating work on "visual indices", in Dana Ballard's notion of deictic codes, and in Kahneman, Treisman, and Wolfe's accounts of systems of evanescent representations they call "object files". Perceptual representation is a layered affair, and I argue that it probably includes both feature-placing and proto-objects. Finally, both nonconceptual systems are contrasted with the full-blooded individuation allowed in a natural language. (shrink)

This paper argues that a theory of situated vision, suited for the dual purposes of object recognition and the control of action, will have to provide something more than a system that constructs a conceptual representation from visual stimuli: it will also need to provide a special kind of direct (preconceptual, unmediated) connection between elements of a visual representation and certain elements in the world. Like natural language demonstratives (such as `this' or `that') this direct connection allows entities to be (...) referred to without being categorized or conceptualized. Several reasons are given for why we need such a preconcep- tual mechanism which individuates and keeps track of several individual objects in the world. One is that early vision must pick out and compute the relation among several individual objects while ignoring their properties. Another is that incrementally computing and updating representations of a dynamic scene requires keeping track of token individuals despite changes in their properties or locations. It is then noted that a mechanism meeting these requirements has already been proposed in order to account for a number of disparate empiri- cal phenomena, including subitizing, search-subset selection and multiple object tracking (Pylyshyn et al., Canadian Journal of Experimental Psychology 48(2) (1994) 260). This mechanism, called a visual index or FINST, is brie. (shrink)

This text aims at presenting a general characterization of the act of perceiving a particular object, in a framework in which perception is conceived of as a mental and cognitive faculty having specific functions that other faculties such as imagination and memory do not possess. I introduce the problem of determining the occurrence of singular perception of a physical object, as opposed to the occurrence of other mental states or attitudes. I propose that clarifying this occurrence problem requires making explicit (...) the conditions of perceptual competence/faculty so as to explain the occurrence of each perceptual performance on the basis of the use of this competence. I argue then for a direct relational model according to which the singular perception of an object depends on a competence of connecting the perceiver directly with each target object. This model is compatible with a disjunctive approach to perception according to which each particular experience of an object corresponds either to a direct perceptual relation with this object or to the illusion of having the experience of this object. The arguments in favour of this relational model rest on the idea that the faculty of perception grounds the capacity to demonstratively identify physical objects. (shrink)

In this paper I challenge the common wisdom (see Dummett and Davidson) that sentences are the minimal units with which one can perform a speech act or make a move in the language game. I thus sit with Perry and Stainton in arguing that subsentences can be used to perform full-fledged speech acts. In my discussion I assume the traditional framework which distinguishes between the proposition expressed and the thought or mental state (possibly a sentence in Mentalese) one comes to (...) grasp when using/understanding an utterance (or sentence-in-a-context) expressing a proposition. Unlike Stainton, I will argue that the proposition expressed by a subsentential assertion and its corresponding thought are not the end product of a pragmatic process of free enrichment. I shall defend the view that a thought may concern something without the thinker having to represent that very thing. This should help us to resist the view that with the utterance of a subsentence enrichment is mandatory. I will further argue that subsentences and their corresponding thoughts are situated. Because of that we can successfully interact and engage in joint ventures using subsentences and be guided by thoughts without having to enrich them. The fact that the actors’ unenriched thoughts are co-situated may suffice to explain the positive outcome of their joint project. Last but not least, I will also show how the picture I propose gains further support by taking on board Perry’s distinction between reflexive truth conditions and incremental truth conditions (or official content). Since competent speakers can grasp an utterance’s reflexive truth conditions without having to grasp its official content (roughly, the proposition expressed) they can successfully interact without their thoughts having to undergo a process of free enrichment. Moreover, if I’m right in arguing that an utterance’s reflexive truth conditions are the best tool to classify the semantic features of one’s mental state (or sentence in Mentalese), we can further explain mental causation and linguistic communication without appealing to free enrichment. (shrink)

In contrast to Constructivist Views, which construe perceptual cognition as an essentially reconstructive process, this article recommends the Deictic View, which grounds perception in perceptual-demonstrative reference and the use of deictic tracking strategies for acquiring and updating knowledge about individuals. The view raises the problem of how sensory-motor tracking connects to epistemic and integrated forms of tracking. To study the strategies used to solve this problem, we report a study of the ability to track distal individuals when only their directions (...) can be perceived and not their locations. We introduce a new experimental paradigm named the 'Modified Traveling Salesman Problem' (MTSP), which requires subjects to visit n invisible targets in a 2D display once each. Surprisingly, subjects are competent at this task for up to 10 targets. We consider two types of tracking strategies that subjects might use: 'location-based' strategies and 'deictic direction-based' strategies. A number of observations suggest that subjects used the latter, at least for larger numbers of targets. We hypothesize that subjects used perceptual-demonstrative reference and deictic strategies (i) to perform the sensory-motor tracking of directional segments, (ii) to bind the segments with their updated status in the task, and (iii) to perform the epistemic tracking of invisible targets by means of perception-based inferences. (shrink)

This review essay critically discusses Andre Kukla's Methods of theoretical psychology. It is argued that Kukla mistakenly tries to build his case for theorizing in psychology as a separate discipline on a dubious distinction between theory and observation. He then argues that the demise of empiricism implies a return of some form of rationalism, which entails an autonomous role for theorizing in psychology. Having shown how this theory-observation dichotomy goes back to traditional and largely abandoned ideas in epistemology, an alternative (...) is presented in the guise of the pragmatist or functionalist tradition, where the interdependence of theory, observation and action is emphasized and the positivist dichotomy of pure observations and pure theory is rejected. Furthermore, we show how recent work on "active" perception supports the functionalist approach. Although the authors agree with Kukla that theory has a legitimate place in psychology, it is suggested that he needlessly limits its scope to autonomous domain-neutral theorizing, and that broadening its perspective to analyzing the presuppositions and implications of empirical work is a more fruitful approach. In fact, the attempt to find the epistemological and philosophical implications of empirical work in perception that is sketched in this review essay is, in the authors' view, a case of theorizing in psychology. (shrink)

Descriptive metaphysics investigates our naïve ontology as this is articulated in the content of our perception or of our pre-reflective thought about the world. But is access to such content reliable? Sceptics about the standard modes of access (introspection, or language-driven intuitions) may think that investigations in descriptive metaphysics can be aided by the controlled findings of cognitive science. Cognitive scientists have studied a promising range of representational advantages, that is, ways in which cognition favours one type of entity over (...) another. The notion of representational advantage is investigated and some scepticism is expressed as to its appropriateness for use in descriptive metaphysics. (shrink)

It is generally accepted that there is something special about reasoning by using mental images. The question of how it is special, however, has never been satisfactorily spelled out, despite more than thirty years of research in the post-behaviorist tradition. This article considers some of the general motivation for the assumption that entertaining mental images involves inspecting a picture-like object. It sets out a distinction between phenomena attributable to the nature of mind to what is called the cognitive architecture, and (...) ones that are attributable to tacit knowledge used to simulate what would happen in a visual situation. With this distinction in mind, the paper then considers in detail the widely held assumption that in some important sense images are spatially displayed or are depictive, and that examining images uses the same mechanisms that are deployed in visual perception. I argue that the assumption of the spatial or depictive nature of images is only explanatory if taken literally, as a claim about how images are physically instantiated in the brain, and that the literal view fails for a number of empirical reasons – for example, because of the cognitive penetrability of the phenomena cited in its favor. Similarly, while it is arguably the case that imagery and vision involve some of the same mechanisms, this tells us very little about the nature of mental imagery and does not support claims about the pictorial nature of mental images. Finally, I consider whether recent neuroscience evidence clarifies the debate over the nature of mental images. I claim that when such questions as whether images are depictive or spatial are formulated more clearly, the evidence does not provide support for the picture-theory over a symbol-structure theory of mental imagery. Even if all the empirical claims were true, they do not warrant the conclusion that many people have drawn from them: that mental images are depictive or are displayed in some (possibly cortical) space. Such a conclusion is incompatible with what is known about how images function in thought. We are then left with the provisional counterintuitive conclusion that the available evidence does not support rejection of what I call the “null hypothesis”; namely, that reasoning with mental images involves the same form of representation and the same processes as that of reasoning in general, except that the content or subject matter of thoughts experienced as images includes information about how things would look. (shrink)

In this paper the relationship between phenomenology of perception and synthetic phenomenology is discussed. Synthetic phenomenology is presented on the basis of the issues in A.I. and Robotics that required to address the question of what enables artificial agents to have phenomenal access to the environment. Phenomenology of perception is construed as a theory with autonomous structure and domain, which can be embedded in a philosophical as well as a scientific theory. Two attempts at specifying the phenomenal content of artificial (...) agents are discussed. Concepts and experimental evidence on the independence of perception and the coordination of motion and appearances are set out to submit that phenomenology of perception makes a contribution to synthetic phenomenology. (shrink)

Most people find it obvious that concepts like APPLE, DOG, WATER, CACTUS, SWIM, CHIRP, FURRY, and SMOOTH are acquired from perceptual experiences along with some kind of inferential procedure. Models of how these concepts are inferentially acquired, however, force the acquired concepts to be representationally complex, built from, and composed by, the more primitive representations. Since at least the time of Plato, philosophers and psychologists have struggled to find complex sets of representations that have the same meanings, definitionally or probabilistically, (...) as these concepts. For example, to think about the property-kind being gold is not the same as to think about the complex property-kind being yellowish & shiny & malleable.... I call this Fodor's Challenge: Find an acquisition process that is genuinely inferential and yields a concept that genuinely is one of these lexical concepts. Rather than continue the pursuit of a complex representation that has the same meaning as our concept GOLD. I offer a model on which many lexical concepts are acquired from perception and inference, without being built up from, and composed by, the representations involved. The model, Baptizing Meanings for Concepts, is inspired in part by Saul Kripke's baptism process for assigning meanings to linguistic terms. Many lexical concepts, according to the BMC, are acquired by inferring the presence a new property-kind, picking out the property-kind in terms of those perceptible features, and then assigning a simple mental term, a concept, for that property-kind. (shrink)

I show how a conversational process that takes simple, intuitively meaningful steps may be understood as a sophisticated computation that derives the richly detailed, complex representations implicit in our knowledge of language. To develop the account, I argue that natural language is structured in a way that lets us formalize grammatical knowledge precisely in terms of rich primitives of interpretation. Primitives of interpretation can be correctly viewed intentionally, as explanations of our choices of linguistic actions; the model therefore fits our (...) intuitions about meaning in conversation. Nevertheless, interpretations for complex utterances can be built from these primitives by simple operations of grammatical derivation. In bridging analyses of meaning at semantic and symbol‐processing levels, this account underscores the fundamental place for computation in the cognitive science of language use. (shrink)

This article compares the ability to track individuals lacking mental states with the ability to track intentional agents. It explains why reference to individuals raises the problem of explaining how cognitive agents track unique individuals and in what sense reference is based on procedures of perceptual-motor and epistemic tracking. We suggest applying the notion of singular-files from theories in perception and semantics to the problem of tracking intentional agents. In order to elucidate the nature of agent-files, three views of the (...) relation between object- and agent-tracking are distinguished: the Independence, Deflationary and Organism-Dependence Views. The correct view is argued to be the latter, which states that perceptual and epistemic tracking of a unique human organism requires tracking both its spatio-temporal object-properties and its agent-properties. (shrink)

A defence of the 'pragmatic' theory of anaphora (which stresses the analogy between anaphora and deixis) against an argument put forward by Gareth Evans.

In this paper I will present three reservations about the claims made by Hutto and Satnet. First of all, though TNOC is presented as drawing on teleological theories of mental content for a conception of Ur-Intentionaltiy, what is separated out after objectionable claims are removed from teleological accounts may not retain enough to give us directed intelligence. This problem raises a question about what we need in a naturalistic basis for an account of the mental. Secondly, I think that the (...) authors’ objections to cognitive science’s supposed notion of a mental representation in fact attack a philosophers’ invention, one that sprung into vibrant being in the mid-1970’s. It is not employed in cognitive neuroscience to any significant extent and it isn’t needed by other disciplines involved in cognitive science. Finally, I worry that the account of the origin of content – namely, explanatory narrative - presents us with a too limited view of human discourse, particularly as it is needed for a social theory of mind. (shrink)

Muchos filósofos piensan que los contenidos perceptuales son siempre generales y que no deben especificarse utilizando términos singulares. Ellos creen que los objetos /propiedades distales no constituyen esencialmente los contenidos perceptuales. Argumentaré que esta estrategia es insatisfactoria al especificar contenidos e incapaz de dar cuenta de una intuición común, según la cual la veracidad de nuestras experiencias perceptuales no es algo evaluable con independencia de si percibimos o no. Finalmente, sugeriré una alternativa "singularista" en la que los objetos distales sí (...) entran en los contenidos, haciendo de las percepciones y las alucinaciones dos tipos de experiencia fundamentalmente diferentes. Many philosophers think that perceptual contents are always general and shouldn´t be specified using singular terms. They believe that distal objects and properties don't essentially constitute perceptual contents. I will argue that this strategy doesn't provide a satisfactory account of content specification and fails to make sense of the common-sense intuition that the veridicality of our perceptual experiences isn't something fully independent of whether we perceive or not. Finally, I will suggest an alternative "singularist" standpoint in which distal objects do enter into visual contents, making perceptions and hallucinations fundamentally different types of experiences. (shrink)

This thesis aims to develop a psychologically plausible account of concepts by integrating key insights from philosophy (on the metaphysical basis for concept possession) and psychology (on the mechanisms underlying concept acquisition). I adopt an approach known as informational atomism, developed by Jerry Fodor. Informational atomism is the conjunction of two theses: (i) informational semantics, according to which conceptual content is constituted exhaustively by nomological mind–world relations; and (ii) conceptual atomism, according to which (lexical) concepts have no internal structure. I (...) argue that informational semantics needs to be supplemented by allowing content-constitutive rules of inference (“meaning postulates”). This is because the content of one important class of concepts, the logical terms, is not plausibly informational. And since, it is argued, no principled distinction can be drawn between logical concepts and the rest, the problem that this raises is a general one. An immediate difficulty is that Quine’s classic arguments against the analytic/synthetic distinction suggest that there can be no principled basis for distinguishing content-constitutive rules from the rest. I show that this concern can be overcome by taking a psychological approach: there is a fact of the matter as to whether or not a particular inference is governed by a mentally-represented inference rule, albeit one that analytic philosophy does not have the resources to determine. I then consider the implications of this approach for concept acquisition. One mechanism underlying concept acquisition is the development of perceptual detectors for the objects that we encounter. I investigate how this might work, by drawing on recent ideas in ethology on ‘learning instincts’, and recent insights into the neurological basis for perceptual learning. What emerges is a view of concept acquisition as involving a complex interplay between innate constraints and environmental input. This supports Fodor’s recent move away from radical concept nativism: concept acquisition requires innate mechanisms, but does not require that concepts themselves be innate. (shrink)

This study provides evidence that eye movements reflect the positions of objects while participants listen to a spoken description, retell a previously heard spoken description, and describe a previously seen picture. This effect is equally strong in retelling from memory, irrespective of whether the original elicitation was spoken or visual. In addition, this effect occurs both while watching a blank white board and while sitting in complete darkness. This study includes 4 experiments. The first 2 experiments measured eye movements of (...) participants looking at a blank white board. Experiment 1 monitors eye movements of participants on 2 occasions: first, when participants listened to a prerecorded spoken scene description; second, when participants were later retelling it from memory. Experiment 2 first monitored eye movements of participants as they studied a complex picture visually, and then later as they described it from memory. The second pair of experiments (Experiments 3 and 4) replicated Experiments 1 and 2 with the only difference being that they were executed in complete darkness. This method of analysis differentiated between eye movements that are categorically correct relative to the positions of the whole eye gaze pattern (global correspondence) and eye movements that are only locally correct (local correspondence). The discussion relates the findings to the current debate on mental imagery. (shrink)

The task of tracking a small number (about four or five) visual targets within a larger set of identical items, each of which moves randomly and independently, has been used extensively to study object-based attention. Analysis of this multiple object tracking (MOT) task shows that it logically entails solving the correspondence problem for each target over time, and thus that the individuality of each of the targets must be tracked. This suggests that when successfully tracking objects, observers must also keep (...) track of them as unique individuals. Yet in the present studies we show that observers are poor at recalling the identity of successfully tracked objects (as specified by a unique identifier associated with each target, such as a number or starting location). Studies also show that the identity of targets tends to be lost when they come close together and that this tendency is greater between pairs of targets than between targets and nontargets. The significance of this finding in relation to the multiple object tracking paradigm is discussed. (shrink)

In this commentary, I will argue that the componential and emergent views of cognitive control as defined by Cooper (2010) do not necessarily oppose each other, and I will try to make a case for their interdependence. First, I will use the construct of cognitive inhibition—one of the main componential control functions mentioned in the target articles—to illustrate my line of reasoning. Then, I will comment on how some of the target articles, each from a different perspective, bring arguments in (...) favor of this integrative view. (shrink)

This article addresses the problem of the nature of mental imagery from a new perspective. It suggests that sign-theoretical approach as elaborated by C. S. Peirce can give a better and more comprehensive explanation of mental imagery. Our empirical findings follow the methodology of cognitive semiotics and they show that (i) properties of mental images are heterogeneous in nature; (ii) properties of mental images are dependent on the characteristics of object-stimulus; (iii) properties of mental images are dependent on individual differences (...) in imaginary capacities. This suggests that, contrary to representational accounts, mental imagery is not based on one dominant representational format. Imagery constitutes a complex system of signs consisting of several sign elements and dynamic relations. A sign-theoretical account may give a better explanation of the nature of mental imagery, as it accommodates heterogenous evidence from this experiment. (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)