Towards a computational theory of experience

A standing challenge for the science of mind is to account for the datum that every mind faces in the most immediate – that is, unmediated – fashion: its phenomenal experience. The complementary tasks of explaining what it means for a system to give rise to experience and what constitutes the content of experience (qualia) in computational terms are particularly challenging, given the multiple realizability of computation. In this paper, we identify a set of conditions that a computational theory must satisfy for it to constitute not just a sufficient but a necessary, and therefore naturalistic and intrinsic, explanation of qualia. We show that a common assumption behind many neurocomputational theories of the mind, according to which mind states can be formalized solely in terms of instantaneous vectors of activities of representational units such as neurons, does not meet the requisite conditions, in part because it relies on inactive units to shape presently experienced qualia and implies a homogeneous representation space, which is devoid of intrinsic structure. We then sketch a naturalistic computational theory of qualia, which posits that experience is realized by dynamical activity-space trajectories (rather than points) and that its richness is measured by the representational capacity of the trajectory space in which it unfolds.     

Neuronal correlates of "free will" are associated with regional specialization in the human intrinsic/default network

Recently, we proposed a fundamental subdivision of the human cortex into two complementary networks-an "extrinsic" one which deals with the external environment, and an "intrinsic" one which largely overlaps with the "default mode" system, and deals with internally oriented and endogenous mental processes. Here we tested this hypothesis by contrasting decision making under external and internally-derived conditions. Subjects were presented with an external cue, and were required to either follow an external instruction ("determined" condition) or to ignore it and follow a voluntary decision process ("free-will" condition). Our results show that a well defined component of the intrinsic system-the right inferior parietal cortex-was preferentially activated during the "free-will" condition. Importantly, this activity was significantly higher than the base-line resting state. The results support a self-related role for the intrinsic system and provide clear evidence for both hemispheric and regional specialization in the human intrinsic system.     

Information processing during face recognition: the effects of familiarity, inversion, and morphing on scanning fixations

Where we make ocular fixations when viewing an object likely reflects interactions between 'external' object properties and internal 'top-down' factors, as our perceptual system tests hypotheses and attempts to make decisions about our environment. These scanning fixation patterns can tell us how and where the visual system gathers information critical to specific tasks. We determined the effects of the internal factors of expertise, experience, and ambiguity on scanning during a face-recognition task, in eight subjects. To assess the effects of expertise, we compared upright with inverted faces, since it is hypothesized that inverted faces do not access an orientation-dependent face-expert processor. To assess the effects of experience, we compared famous with novel faces, as famous faces would have stronger internal representations than anonymous ones. Ambiguity in matching seen and remembered faces was manipulated with morphed faces. We measured three classes of variables: (i) total scanning time and fixations; (ii) the spatial distribution of scanning; and (iii) the sequence of scanning, using first-order Markov matrices for local scan structure and string editing for global scan structure. We found that, with inverted faces, subjects redistributed fixations to the mouth and lower face, and their local and global scan structure became more random. With novel or morphed faces, they scanned the eyes and upper face more. Local scan structure was not affected by familiarity, but global scan structure was least random (most stereotyped) for novel upright faces. We conclude that expertise (upright faces) leads to less lower-face scanning and more predictable global patterns of information gathering. Experience (famous faces) leads to less upper-face scanning and more idiosyncratic global scan structures, suggesting a superseding influence of facial memories. With morphed faces, subjects return to the upper face to resolve ambiguity, implying a greater importance of this region in face recognition.     

From rotation to disfiguration: testing a dual-strategy model for recognition of faces across view angles

A study is reported of the effect of distinctive marks on the recognition of unfamiliar faces across view angles. Subjects were asked to memorize a set of target faces, half of which had distinctive marks. Recognition was assessed by presenting the target faces, either in the same orientation, or after 90 degrees rotation, mixed with an equal number of distractors. Results show that the effect of distinctive marks depends on the view presented during learning. When a frontal view was learned, as predicted by the dual-strategy model [Valentin et al, in press, in Computational, Geometric, and Process Perspectives on Facial Cognition: Context and Challenges Eds T Wenger, J Townsend (Hillsdale, NJ: Lawrence Erlbaum Associates)], distinctive marks improve recognition performance in the 90 degrees condition but not in the 0 degree condition. However, when a profile view was learned, distinctive marks have no effect on recognition performance, even in the 90 degrees condition where a frontal view is tested.     

Compliance during sessions and homework in exposure-based treatment of agoraphobia

The relationship between compliance with cognitive-behavioral treatment instructions and outcome was examined for 56 agoraphobic clients treated with in vivo exposure and training in anxiety management strategies. Clients who complied more often with anxiety management instructions during treatment sessions tended to improve more on a behavioral avoidance test than those who were less compliant, but did not differ on three other outcome variables. Compliance with instructions for self-directed exposure between sessions was examined in a subset of 28 of these Ss. Clients who spent more time doing homework reported significantly greater decrements in fear of fear than less compliant clients and also tended to report larger changes on avoidance behavior. However, a quasi-experimental comparison of homework vs no-homework treatment protocols yielded no difference in outcome. Less compliant clients were more symptomatic pretreatment and rated their therapists as less caring and less self-confident.