Consciousness is, perhaps, the aspect of our mental lives that is the most perplexing for both psychologists and philosophers. Daniel Dennett has described it as 'both the most obvious and the most mysterious feature of our minds' and attempts at definition often seem to move in circles. Thomas Nagel famously remarked that 'without consciousness the mind-body problem would be much less interesting. With consciousness it seems hopeless.' These observations might suggest that consciousness - indefinable and mysterious - falls outside the (...) scope of rational enquiry, defying both scientific and philosophical investigation. In reality, however, the topic has been a focus of psychological investigation since William James and is increasingly vital in philosophical research. This book illustrates the various, interdisciplinary approaches to the problem, providing both pointers to a solution and a summary of the key positions. (shrink)

Category-specific impairments of object recognition and naming are among the most intriguing disorders in neuropsychology, affecting the retrieval of knowledge about either living or nonliving things. They can give us insight into the nature of our representations of objects: Have we evolved different neural systems for recognizing different categories of object? What kinds of knowledge are important for recognizing particular objects? How does visual similarity within a category influence object recognition and representation? What is the nature of our semantic knowledge (...) about different objects? We review the evidence on category-specific impairments, arguing that deficits even for one class of object cannot be accounted for in terms of a single information processing disorder across all patients; problems arise at contrasting loci in different patients. The same apparent pattern of impairment can be produced by damage to different loci. According to a new processing framework for object recognition and naming, the hierarchical interactive theory, we have a hierarchy of highly interactive stored representations. HIT explains the variety of patients in terms of lesions at different levels of processing and different forms of stored knowledge used both for particular tasks and for particular categories of object. Key Words: category-specific deficits; functional imaging; hierarchical models; interactive activation models; neuropsychology; object recognition; perceptual and functional knowledge. (shrink)

We present work demonstrating that the nature of an object for our visual system depends on the actions we are programming and on the presence of action relations between stimuli. For example, patients who show visual extinction are more likely to become aware of two objects if the objects fall in appropriate visual locations for a common action. This effect of the action relations between objects is modulated both by the familiarity of the positioning of the objects for action, and (...) by the mere possibility of action (the ‘affordance’) between the objects. In addition, the programming of an action to a part of an object alters the representation of that object, making the ‘part’ into the object selected by the visual system. These results point to object coding being a rather flexible process, affected not only by the perceptual properties of stimuli but also by the relations between these properties and action. We discuss the implications for theories of perception as well as considering why action information, in particular, may be important for perception. (shrink)

We summarise and respond to the main points made by the commentators on our target article, which concern: whether structural similarity can play a causal role in normal object identification and in neuropsychological deficits for living things, the nature of our structural knowledge of the world, the relations between sensory and functional knowledge of objects, and the nature of our functional knowledge about living things, whether we need to posit a “core” semantic system, arguments that can be marshalled from evidence (...) on functional imaging, the causal mechanisms by which category differences can emerge in object representations, and the nature of our knowledge about categories other than living and nonliving things. We also highlight points raised in our article that seem to be accepted. (shrink)

We discuss the difficulty of measuring the perceptual experience of colour, supporting Palmer's assertion that neuropsychological disorders of colour processing can be informative in this respect. We point out that some disorders seem to affect the perceptual experience of colour over and above the perceptual processing of colour, providing direct insights into the neural mechanisms supporting perceptual experience.

An efficient representation of the environment requires both the selection of a fraction of the information that reaches our senses and the organization of this information into coherent and meaningful elements. Here we discuss the dynamic interplay between selective attention and perceptual organization, important processes that allow us to perceive a seamless, integrated world. Based on evidence from behavioral and neuroimaging studies with normal observers and neuropsychological patients, we examine whether: perceptual grouping constrains visual attention, determining which objects will be (...) selected and be candidates for explicit report; visual attention modulates perceptual grouping, determining how elements are grouped to form meaningful wholes. The data suggest that, whilst not being necessary for at least some forms of perceptual grouping, visual attention can nevertheless modulate grouping. We conclude that selection is dynamically set by bottom-up stimulus factors, top-down knowledge and the allocation of attention to space and within grouped regions of objects. (shrink)

Evidence from visual-search experiments is discussed that indicates that there is spatially parallel encoding based on three-dimensional (3-D) spatial relations between complex image features. In one paradigm, subjects had to detect an odd part of cube-like figures, formed by grouping of corner junctions. Performance with cube-like figures was unaffected by the number of corner junctions present, though performance was affected when the corners did not configure into a cube. It is suggested from the data that junctions can be grouped to (...) form 3-D shapes in a spatially parallel manner. Further, performance with cube-like figures was more robust to noncollinearity between junctions than was performance when junctions grouped to form two-dimensional planes. In the second paradigm, subjects searched for targets defined by their size. Performance was affected by a size illusion, induced by linear-perspective cues from local background neighbourhoods. Search was made more efficient when the size illusion was consistent with the real size difference between targets and nontargets, and it was made less efficient when the size illusion was inconsistent with the real size difference. This last result occurred even though search was little affected by the display size in a control condition. We suggest that early, parallel visual processes are influenced by 3-D spatial relations between visual elements, that grouping based on 3-D spatial relations is relatively robust to noncollinearity between junctions, and that, at least in some circumstances, 3-D relations dominate those coded in two-dimensions. (shrink)

The current conceptualization of working memory highlights its pivotal role in the cognitive control of goal-directed behaviour, for example, by keeping task-priorities and relevant information ‘online’. Evidence has accumulated, however, that working memory contents can automatically misdirect attention and observers can only exert little intentional control to overcome irrelevant contents held in memory that are known to be misleading for behaviour. The authors discuss extant evidence on this topic and argue that obligatory functional coupling between working memory and attentional selection (...) reflects a default property of the brain which is hardwired in overlapping substrates for memory and perception. They further argue that the neuroanatomical substrates for working memory biases in vision are distinct from the classical fronto-parietal networks involved in attentional control and distinct from the mechanisms that mediate attention biases from long-term memory. Finally the authors present emerging evidence that working memory ‘guiding’ processes may operate outside conscious awareness. (shrink)

Prior work shows that the possibility of action to an object facilitates attentional deployment. We sought to investigate the neural mechanisms underlying this modulation of attention by examining ERPs to target objects that were either congruently or incongruently gripped for their use in the presence of a congruently or incongruently gripped distractor. Participants responded to the presence or absence of a target object matching a preceding action word with a distractor object presented in the opposite location. Participants were faster in (...) responding to congruently gripped targets compared to incongruently gripped targets. There was a reduced N2pc potential when the target was congruently gripped, and the distractor was incongruently gripped compared to the conditions where targets were incongruently gripped or when the distractor, as well as target, was congruently gripped. The N2pc results indicate that target selection is easier when action information is congruent with an object’s use. (shrink)