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.

Smaller latency costs for switching from dominant (habitual) to non-dominant (unusual) tasks compared to the reverse direction have been noted in some studies of task-switching. This asymmetry has been cited as evidence of inhibitory effects from the prior trial. We examined accuracy and latency costs of task-switching between prosaccades and antisaccades, where task-switching is limited to stimulus-response re-mapping and occurs between tasks highly asymmetric in dominance. Eighteen subjects executed prosaccades and antisaccades in single-task and mixed-task blocks. In mixed-task blocks, antisaccade and prosaccade trials were ordered randomly, resulting in 'repeated' trials that were preceded by the same type of trial (i.e. antisaccade-antisaccade), and 'switched' trials that were preceded by the opposite type of trial. Comparisons of the single-task blocks and repeated trials of the mixed-task blocks indexed the mixed-list costs, which were small for prosaccades and insignificant for antisaccades. Comparison of the repeated and switched trials from the mixed-task blocks indexed the residual task-switch cost. Accuracy costs of task-switching and antisaccades were equivalent. The accuracy of trials incorporating both switching and antisaccades in a single response (i.e. switched antisaccade) equalled the product of the accuracies of doing each operation alone, supporting independence of these two functions. In contrast, the latency cost of antisaccade performance was 3 times greater than that of task-switching. Task-switching from prosaccades to antisaccades resulted in a paradoxical decrease in antisaccade latency. This decrease correlated with other indices of vigilance, with the paradoxical effect minimized in more attentive observers. The latency data suggest that either an antisaccade on the prior trial perturbs saccadic responses more than a task-switch, or concurrent task-switching specifically facilitates antisaccades. In either case, the paradoxical benefit of task-switching for antisaccades challenges current models of task-switching.

Impaired perception of spatial relations in prosopagnosia is selective to the spatial structure within individual objects and spares the perception of spatial location of objects. It is not specific to faces. It reveals a process involved in analyzing object structure, consistent with the patients' deficits in recognizing facial identity, and illustrates a different type of "visuospatial" defect.

Although there is compelling evidence suggesting that frontostriatal dysfunction may be central to the pathophysiology of ADHD, the neuroimaging findings point to distributed neural substrates rather than a single one. More research is needed to elucidate the nature of contributions of nonfrontostriatal regions to the pathophysiology of ADHD.

Extensive right occipitotemporal lesions with significant deficits in face perception are not incompatible with covert face processing. Covert processing is absent in developmental prosopagnosia, because this condition likely precludes the establishment of a store of accurate facial memories. The presence of covert processing correlates with the degree of residual overt familiarity, indicating that these are related phenomena.

It has been hypothesized that social developmental disorders (SDD) like autism, Asperger's disorder and the social-emotional processing disorder may be associated with prosopagnosic-like deficits in face recognition. We studied the ability to recognize famous faces in 24 adults with a variety of SDD diagnoses. We also measured their ability to discriminate changes in internal facial configuration, a perceptual function that is important in face recognition, and their imagery for famous faces, an index of their facial memory stores. We contrasted their performance with both healthy subjects and prosopagnosic patients. We also performed a cluster analysis of the SDD patients. One group of eight SDD subjects performed normally on all tests of face perception and recognition. The other 16 subjects were impaired in recognition, though most were better than prosopagnosic patients. One impaired SDD subgroup had poor perception of facial structure but relatively preserved imagery, resembling prosopagnosic patients with medial occipitotemporal lesions. Another subgroup had better perception than imagery, resembling one prosopagnosic with bilateral anterior temporal lesions. Overall, SDD subgroup membership by face recognition did not correlate with a particular SDD diagnosis or subjective ratings of social impairment. We conclude that the social disturbance in SDD does not invariably lead to impaired face recognition. Abnormal face recognition in some SDD subjects is related to impaired perception of facial structure in a manner suggestive of occipitotemporal dysfunction. Heterogeneity in the perceptual processing of faces may imply pathogenetic heterogeneity, with important implications for genetic and rehabilitative studies of SDD.

No abstract

Although anterior temporal cortex may be the site of facial memory stores, these data also support hypotheses that perceptual areas like the fusiform face area have parallel contributions to mental imagery. The data on covert recognition are consistent with a view that it is the residue of a partially damaged face-recognition network. Covert recognition may reflect the degree of damage across components of a network rather than mark a specific form of prosopagnosia or a dissociated pathway.