Visual perception and its impairment in schizophrenia

Abstract

Much work in the cognitive neuroscience of schizophrenia has focused on attention, memory, and executive functioning. To date, less work has focused on perceptual processing. However, perceptual functions are frequently disrupted in schizophrenia, and thus this domain has been included in the CNTRICS (Cognitive Neuroscience Treatment Research to Improve Cognition in Schizophrenia) project. In this article, we describe the basic science presentation and the breakout group discussion on the topic of perception from the first CNTRICS meeting, held in Bethesda, Maryland on February 26 and 27, 2007. The importance of perceptual dysfunction in schizophrenia, the nature of perceptual abnormalities in this disorder, and the critical need to develop perceptual tests appropriate for future clinical trials were discussed. Although deficits are also seen in auditory, olfactory, and somatosensory processing in schizophrenia, the first CNTRICS meeting focused on visual processing deficits. Key concepts of gain control and integration in visual perception were introduced. Definitions and examples of these concepts are provided in this article. Use of visual gain control and integration fit a number of the criteria suggested by the CNTRICS committee, provide fundamental constructs for understanding the visual system in schizophrenia, and are inclusive of both lower-level and higher-level perceptual deficits.

Figure 1

(A) Architecture of the early visual system [left part adapted by permission from Macmillan Publishers Ltd: Nat Rev Neurosci 8:276–286, copyright 2007 (87); (B) Visual cortical processing streams. LGN, lateral geniculate nucleus; Pulv, pulvinar; SC, superior colliculus.

Figure 2

Gain control can contribute to orientation “pop-out.” In this example, the top row of the right side of the figure shows the “raw” neural response where gain control is not operating. In the bottom row, divisive gain control is operating and the large number of neighboring neurons that receive the same horizontal stimulus inhibit each other and decrease signaling, allowing the response from the small diagonally textured patch to “pop out.” Under this view the visual system operates as a cascaded gain-control/integration system, deriving increasingly complex types of salience.

Figure 3

Contrast response functions and N-methyl d-aspartate (NMDA) effects ([A]. Adapted from Kwon et al. [16], used with permission; [B and C] adapted from Butler et al. Arch Gen Psychiatry, May 2005, 62, 495–504, copyright © 2005, American Medical Association, all rights reserved [22]). The NMDA antagonists produce shallower gain at low contrast and a much lower plateau in visual evoked potential responses indicating decreased signal amplification. The patient visual evoked potential contrast response curve in the magnocellular condition shows similar decreased gain at low luminance contrast and a lower plateau, indicating decreased signal amplification.

Figure 4

Contextual effects on orientation (reprinted from Neuron, 48, Dakin S and Frith U, Vagaries of visual perception in autism, 497–507, copyright 2005, with permission from Elsevier [88]). Oriented structure within our complex visual environment leads to various types of interactions between detectors in V1 (blue region), including integration (“+” connections) and gain control (“−” connections).

Figure 5

The “contrast-contrast” illusion reveals contrast gain control deficits in schizophrenia (reprinted from Curr Biol, 15, Dakin S, Carlin P, Hemsley D, Weak suppression of visual context in chronic schizophrenia, R822–824, copyright 2005, with permission from Elsevier [27]). (A) The small region at the center of the large circular patch is physically identical to the small patch at the top left but generally seems to be of much lower contrast as a consequence of contrast gain control. (B) One can quantify this effect by plotting the probability that subjects said the central patch was higher contrast than a matching variable contrast reference patch. A typical control subject (green line) indicated that the central patch had a substantially lower contrast than it actually did (indicated by the shift in the green curve to lower reference contrasts). Data from a representative patient with schizophrenia (red line) indicated that they were not susceptible to the illusion and matched the contrast largely correctly.

Figure 6

Performance of the schizophrenia group (dashed line) and healthy control group (solid line) across six conditions of contour element jitter manipulation. The subject's task was to indicate, with a two-button response device, on each trial, whether the narrow part of the egg-shaped contour is pointing to the left or the right. With increasing element jitter (± the number of degrees noted on the x axis), the correlations between adjacent contour elements decrease, and perception of the contour amidst dense background noise becomes more difficult. The left-hand side shows the increasing element jitter of the adjacent contours amidst the background noise. Schizophrenia patients were not able to perform at above chance levels in the two most difficult conditions (reprinted from Computers in Human Behavior, 22, Kozma-Wiebe P, et al., Development of a world-wide web based contour integration test, 971–980, 2006, with permission from Elsevier [65]).