Biomedical subjects

Mariya V Cherkasova

Publications and source records attributed to Mariya V Cherkasova.

11 recordsLinked to original sources

PubMed2006

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.

Adult↗

PubMed2005

Impaired spatial coding within objects but not between objects in prosopagnosia.

BACKGROUND: Patients with prosopagnosia from occipitotemporal lesions have impaired perception of the configuration of facial features. This may be an example of impaired "within-object" spatial coding, which others propose to be distinct from "between-object" spatial coding. OBJECTIVE: To determine whether the prosopagnosic deficit in perceiving spatial configuration was specific to within-face and not between-face spatial coding and whether the deficit was face-selective or extended to objects other than faces. METHODS: Six prosopagnosic patients were tested using an oddity paradigm in which they detected which of three simultaneously seen stimuli was an altered target. In the "within-face" task, the target face had altered interocular distance or mouth position. In the "between-face" task, the target face was located farther away from the other two. In the "within-object" task, the stimulus was a two-dot pattern, and the target pattern had altered interdot distance. RESULTS: Spatial judgments were impaired within faces for all six patients and within the two-dot pattern for five of six patients. However, all six had normal between-face spatial perception. CONCLUSIONS: 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.

Adult↗

PubMed2005

What is perseverated in schizophrenia? Evidence of abnormal response plasticity in the saccadic system.

Although perseveration is sometimes attributed to defective set switching, the authors have recently shown that set-switching is normal in schizophrenia. In this article, the authors tested for persistent states of the saccadic response system, rather than set perseveration. Schizophrenic and healthy subjects performed antisaccades and prosaccades. The authors analyzed for 3 carry-over effects. First, whereas the latency of the current saccade correlated with that of the prior saccade in both groups, the correlations under mixed-task conditions declined in healthy but not in schizophrenic subjects. Second, antisaccades in penultimate trials delayed upcoming saccades in schizophrenic but not in healthy subjects. Third, schizophrenic subjects were more likely to erroneously perseverate the direction of a prior antisaccade but not a prior prosaccade. The authors concluded that, in schizophrenia, the effects of correct antisaccades are persistent not weak. Saccades in schizophrenia are characterized by perseveration of antisaccade-induced changes in the saccadic response system rather than failures to switch task set.

Adult↗

PubMed2004

The covert priming effect of faces in prosopagnosia.

BACKGROUND: There are many methods of testing covert face recognition in prosopagnosia, but it is not clear whether different types of covert recognition share a common mechanism. OBJECTIVE: To determine whether direct forced-choice techniques and indirect face-priming methods yielded similar behavioral estimates of covert ability in a series of prosopagnosic patients. METHODS: The authors tested seven control subjects and seven prosopagnosic patients. Six patients had an apperceptive prosopagnosia: one with childhood onset, three with bilateral lesions, and two with unilateral occipitotemporal lesions. The last had an associative prosopagnosia from bilateral anterior temporal lesions. The direct tests of covert function involved sorting faces by occupation or the forced choosing of which of two faces was famous with a name cue. The indirect test assessed name classification by occupation after priming with a facial stimulus. RESULTS: In normal subjects, the chief priming effect was facilitation by the true face. In the six patients with apperceptive prosopagnosia, direct covert measures were correlated with the face-priming effect, with better covert ability in patients with unilateral posterior lesions. In the patient with associative prosopagnosia, there was a dissociation between excellent direct covert function and absent face priming. CONCLUSIONS: Direct and indirect covert functions likely share similar mechanisms in patients with apperceptive prosopagnosia and may reflect residual activity in anterior and left hemispheric components of the normal face-processing network. However, face priming may be ineffectual in patients with severely degraded facial memories from anterior temporal damage. This may indicate a difference between residual patterns of face-related activity in associative and apperceptive prosopagnosia.

Adult↗

PubMed2004

The relationship of saccadic peak velocity to latency: evidence for a new prosaccadic abnormality in schizophrenia.

Antisaccades have not only longer latencies but also lower peak velocities than prosaccades. It is not known whether these latency and velocity differences are related. Studies of non-human primates suggest that prosaccade peak velocity declines as latency from target appearance increases. We examined whether a similar relationship between peak velocity and latency existed in human saccades, whether it accounted for the difference in peak velocity between antisaccades and prosaccades, and whether it was affected by schizophrenia, a condition that affects antisaccade performance. Sixteen control and 21 schizophrenia subjects performed prosaccade and antisaccade trials in the same test session. In both groups antisaccades had lower peak velocities than prosaccades. Latency did not influence the peak velocities of antisaccades in either subject group. At short latencies, the peak velocities of prosaccades were also similar in the two groups. However, while prosaccade peak velocities declined minimally with increasing latency in control subjects, those in the schizophrenia group declined significantly until they reached a value similar to antisaccade peak velocities. We conclude that, in normal subjects, the effect of latency on prosaccade peak velocity is minimal and cannot account for the lower velocity of antisaccades. In schizophrenia, we hypothesize that the latency-related decline in prosaccade peak velocity may reflect either an increased rate of decay of the effect of the transient visual signal at the saccadic goal, or a failure of the continuing presence of the target to sustain neural activity in the saccadic system.

Adult↗

PubMed2004

Are patients with social developmental disorders prosopagnosic? Perceptual heterogeneity in the Asperger and socio-emotional processing disorders.

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.

Adolescent↗

PubMed2004

Perceptual functions in prosopagnosia.

Some patients with prosopagnosia may have an apperceptive basis to their recognition defect. Perceptual abnormalities have been reported in single cases or small series, but the causal link of such deficits to prosopagnosia is unclear. Our goal was to identify candidate perceptual processes that might contribute to prosopagnosia, by subjecting several prosopagnosic patients to a battery of functions that may be necessary for accurate facial perception. We tested seven prosopagnosic patients. Three had unilateral right occipitotemporal lesions, two had bilateral posterior occipitotemporal lesions, and one had right anterior-to-occipital temporal damage along with a small left temporal lesion. These lesions all included the fusiform face area, in contrast to one patient with bilateral anterior temporal lesions. Most patients had impaired performance on face-matching tests and difficulty with subcategory judgments for non-face objects. The most consistent deficits in patients with lesions involving the fusiform face area were impaired perception of spatial relations in dot patterns and reduced contrast sensitivity in the 4 to 8 cycles deg(-1) range. Patients with bilateral lesions were impaired in saturation discrimination. Luminance discrimination was normal in all but two patients, and spatial resolution was uniformly spared. Curvature and line-orientation discrimination were impaired in only one patient, who also had the most difficulty with more basic-level object recognition. We conclude that deficits in luminance, spatial resolution, curvature, line orientation, and contrast at low spatial frequencies are unlikely to contribute to apperceptive prosopagnosia. More relevant may be contrast sensitivity at higher spatial frequencies and the analysis of object spatial structure. Deficits in these functions may impair perception of subtle variations in object shape, and may be one mechanism by which the recognition defect in prosopagnosia can extend to other classes of object subcategorization.

Adult↗

PubMed2003

Developmental prosopagnosia: a study of three patients.

We studied perception in three patients with prosopagnosia of childhood onset. All had trouble with other 'within-category' judgments. All were deficient on face matching tests and severely impaired on tests of perception of the spatial relations of facial features and abstract designs, indicating a deficit in the encoding of coordinate relationships, similar to adult-onset prosopagnosia with lesions of the fusiform face area. Two had difficulty perceiving feature colour, which correlated with reduced luminance sensitivity. In contrast to adult-onset patients, saturation discrimination was spared in two and spatial resolution impaired in two. Curvature discrimination was relatively spared. Contrast sensitivity showed variable reductions at different spatial frequencies. We conclude that developmental prosopagnosia is similar to the adult-onset form in encoding deficits for the spatial arrangement of facial elements. Deficits in luminance perception and spatial resolution are more associated with defective encoding for basic object-level recognition, as shown on tests of object and spatial perception.

Adult↗

PubMed2002

Schizophrenic subjects show deficient inhibition but intact task switching on saccadic tasks.

BACKGROUND: Schizophrenic patients have executive function deficits, presumably on the basis of prefrontal cortex dysfunction. Although they consistently show impaired inhibition, the evidence of a task switching deficit is less consistent and is often based on performance of neuropsychological tests that require several cognitive processes (e.g., the Wisconsin Card Sort Test [WCST]). We investigated inhibition and task switching using saccadic tasks to determine whether schizophrenic patients have selective impairments of these executive functions. METHODS: Sixteen normal and 21 schizophrenic subjects performed blocks of randomly mixed prosaccade and antisaccade trials. This gave rise to four trial types: prosaccades and antisaccades that were either repeated or switched. Response accuracy and latency were measured. Schizophrenic subjects also performed the WCST. RESULTS: Schizophrenic subjects showed abnormal antisaccade and WCST performance. In contrast, task switching was normal and unrelated to either antisaccade or WCST performance. CONCLUSIONS: The finding of intact task switching performance that is unrelated to other measures of executive function demonstrates selective rather than general impairments of executive functions in schizophrenia. The findings also suggest that abnormal WCST performance is unlikely to be a consequence of deficient task switching. We hypothesize that inhibition and task switching are mediated by distinct neural networks, only one of which is dysfunctional in schizophrenia.

Adult↗

PubMed2002

Antisaccades and task-switching: interactions in controlled processing.

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.

Adolescent↗

PubMed2002

Antisaccades and task switching: studies of control processes in saccadic function in normal subjects and schizophrenic patients.

Executive functions allow us to respond flexibly rather than stereotypically to the environment. We examined two such functions, task switching and inhibition in the antisaccade paradigm, in two studies. One study involved 18 normal subjects; the other, 21 schizophrenic patients and 16 age-matched controls. Subjects performed blocks of randomly mixed prosaccades and antisaccades. Repeated trials were preceded by the same type of trial (i.e., an antisaccade following an antisaccade), and switched trials were preceded by a trial of the opposite type. We measured accuracy rate and latency as indices of processing costs. Whereas schizophrenic patients had a threefold increase in error rate for antisaccades compared to normals, the effect of task switching on their accuracy did not differ from that in normal subjects. Moreover, the accuracy rate of trials combining antisaccade and task switching was equivalent to a multiplication of the accuracy rates from trials in which each was done alone. Schizophrenic latencies were disproportionately increased for antisaccades, but again they were no different from normal subjects in the effect of task switching. In both groups the effect of task switching on antisaccades was a paradoxical latency reduction. We conclude that the executive dysfunction in schizophrenia is not generalized but selective, sparing task switching from exogenous cues, in which the switch is limited to a stimulus-response remapping. The accuracy data in both groups support independence of antisaccade and task-switching functions. The paradoxical task-switching benefit in antisaccadic latency effects challenges current models of task switching. It suggests either carryover inhibition by antisaccadic performance in the prior trial or facilitation of antisaccades by simultaneous performance of other cognitive operations.

Attention↗