Psychological assessment of catatonic schizophrenia

Probably due to the rarity of the disorder and the general inability of catatonic patients to cooperate with standardized assessment, no data exist documenting the psychological features associated with catatonic schizophrenia that may appear on psychological tests. This study utilized standard assessment techniques to examine clinical hypotheses regarding the psychogenic correlates of catatonic conditions from the performance of one man on psychological tests. In accordance with previous theory, test findings indicated frequent constriction, rigidity, and negativism in conjunction with compulsive traits. Experiences of cognitive and self-fragmentation were juxtaposed with a formal, mechanistic body ego; disorganization and discontinuity were countered with attempts at self-cohesion. Depressed feelings and human interest were apparent, although interpersonal relatedness was frequently characterized by an avoidant, distancing style.     

Negative priming in same-different matching: further evidence for a central locus of inhibition

Responses to recently ignored information may be slower or less accurate than responses to information not recently encountered. Such negative priming effects imply that the mechanism of selective attention operates on unattended, as well as attended, information. In the present experiment, subjects judged the second and fourth letters of five-letter strings (e.g., BABAB) as "same" or "different." Responses were slower when a target letter was identical to the distractors presented in the immediately preceding trial. This effect did not depend on which response was required on the current or preceding trial. The results suggest that ignored information is functionally disconnected from the response system as a whole, rather than from a specific response.     

An asymmetry in transmodal perceptual learning

Transmodal perceptual learning was examined in a canonical same/different paradigm. Subjects naive to vibrotactile stimulation and unfamiliar with the task were asked to discriminate sequentially presented shapes moving laterally across an aperture. On all trials, the shapes were presented either visually and then vibrotactually or in the opposite modality order, and on all trials the shapes moved in opposite directions. Analyses of the data revealed that although perceptual learning was evident in both groups, the rate of the learning was more rapid in the visual-vibrotactile group. This interaction of modality order and practice was significant and was considered in terms of E.J. Gibson's theory of perceptual learning and in terms of the constructs, suggested by J.J. Gibson, of available and accessible information-in-stimulation and the education of attention.     

The relation between color spreading and illusory contours

In the present study, we examine the relation between neon color spreading (Redies & Spillmann, 1981) and illusory contours. In Experiment 1, the effects of misalignment between the line elements on the illusory contours in the Ehrenstein figure and in the Redies-Spillmann figure were examined. The remarkable overlap of the two curves for the likelihood of perceiving illusory contours in the Ehrenstein figure and in the Redies-Spillmann figure suggests that the illusory contours surrounding brightness enhancement (Ehrenstein, 1941) and those surrounding neon color spreading are caused by the same mechanism. We further examined both the effects of the interposed grids seen either in front of or behind the figures (Experiment 2) and the effects of misalignment (Experiment 3) on the illusory contours and range of color spreading, and found a high correlation between the appearance/disappearance of illusory contours and global/local color spreading. In Experiment 4, we added new lines to induce illusory contours to the line elements inducing local color spreading. We found that global color spreading was seen to cover the area surrounded by the illusory contours. On the basis of these findings, we suggest that there is an interaction between illusory contours and local color spreading.     

Letter identification declines with increasing retinal eccentricity at the same rate for normal and dyslexic readers

It has recently been claimed (Geiger & Lettvin, 1987; Perry, Dember, Warm, & Sacks, 1989) that the acuity/eccentricity function is flatter in dyslexics than in normal subjects, with dyslexics showing better performance in the periphery and worse performance at fixation. In these studies, all target letters were presented to the right of fixation, a procedural flaw inviting subjects to optimize performance by directing attention and/or gaze to the right of the designated fixation point. It is suggested that dyslexic and normal readers may differ in the degree to which they might adopt the optimal strategy in this situation. To overcome this problem, target letters were briefly presented at 16 randomly intermixed locations derived from the orthogonal combination of four eccentricities and four directions from fixation (above, below, right, left). The accuracy of letter identification declined with increasing eccentricity at the same rate for good and poor adult readers and dyslexic teenagers. This finding provides no support for the view that the acuity/eccentricity function might vary with and possibly cause differences in reading level.     

The effects of temporal modulation and spatial location on the perceived spatial frequency of visual patterns

The perceived spatial frequency of a visual pattern can increase when a pattern drifts or is presented at a peripheral visual field location, as compared with a foveally viewed, stationary pattern. We confirmed previously reported effects of motion on foveally viewed patterns and of location on stationary patterns and extended this analysis to the effect of motion on peripherally viewed patterns and the effect of location on drifting patterns. Most central to our investigation was the combined effect of temporal modulation and spatial location on perceived spatial frequency. The group data, as well as the individual sets of data for most observers, are consistent with the mathematical concept of separability for the effects of temporal modulation and spatial location on perceived spatial frequency. Two qualitative psychophysical models suggest explanations for the effects. Both models assume that the receptive-field sizes of a set of underlying psychophysical mechanisms monotonically change as a function of temporal modulation or visual field location, whereas the perceptual labels attached to a set of channels remain invariant. These models predict that drifting or peripheral viewing of a pattern will cause a shift in the perceived spatial frequency of the pattern to a higher apparent spatial frequency.     

The role of discontinuities in the perception of subjective figures

Recently we proposed a theory of visual interpolation (Kellman & Shipley, in press) that addresses a variety of unit formation phenomena, including the perception of partly occluded objects and subjective figures. A basic notion of the theory is that discontinuities in the first derivative of projected edges are the initiating conditions for interpolation of boundaries that are not physically specified. In this paper, we report four experiments in which this claim was tested in the domain of subjective figures. Experiments 1 and 2 demonstrate that discontinuities in the first derivative of the edges of inducing elements have a clear effect on the frequency of report and the perceived clarity of simple subjective figures. Similar effects are found when unfamiliar subjective figures and inducing elements are used (Experiment 3). Experiment 4 rules out the possibility that the discontinuities in the first derivative merely add to the clarity of subjective figures. These experiments suggest that first-order discontinuities play a central role in unit formation.     

Relationship of induced motion and apparent straight-ahead shifts to optokinetic stimulus velocity

Induced motion (IM) of a fixated spot stimulus and shifts of the apparent straight-ahead (ASA) from the objective median plane were studied as a function of the velocity of a full-field optokinetic background stimulus. Both IM and ASA were influenced similarly by changes in stimulus velocity. The magnitude of both responses, averaged across subjects, increased to a peak level with background velocities of 40-80 deg/sec and decreased at higher velocities. Individual subjects differed with respect to the precise functions by which IM and ASA shifts were related to stimulus velocity. However, for individual subjects, the effects of velocity on IM and ASA shifts were typically highly correlated. Although IM is correlated with shifts of ASA in the opposite direction, the magnitude of the ASA shift is insufficient to account for the observed IM.