William A. Phillips

On the distinction between sensory storage and short-term visual memory

A pattern made by randomly filling cells in a square matrix was presented for 1 see and followed, after various intervals, by an identical or similar pattern. Ss responded “same” or “different.” Performance was fast and accurate if the interval was short and there was no movement or masking of the pattern during the interval. Performance was slower, less accurate, and highly dependent on pattern complexity if the interval exceeded 100 msec or if there was movement or masking. The results are interpreted as evidence for two distinct classes of visual memory: high-capacity sensory storage which is tied to spatial position and is maskable and brief; and schematic short-term visual memory which is not tied to spatial position, which is protected against masking, and which becomes less effective over the first few seconds but not over the first 600 msec.

Convergence of biological and psychological perspectives on cognitive coordination in schizophrenia.

The concept of locally specialized functions dominates research on higher brain function and its disorders. Locally specialized functions must be complemented by processes that coordinate those functions, however, and impairment of coordinating processes may be central to some psychotic conditions. Evidence for processes that coordinate activity is provided by neurobiological and psychological studies of contextual disambiguation and dynamic grouping. Mechanisms by which this important class of cognitive functions could be achieved include those long-range connections within and between cortical regions that activate synaptic channels via NMDA-receptors, and which control gain through their voltage-dependent mode of operation. An impairment of these mechanisms is central to PCP-psychosis, and the cognitive capabilities that they could provide are impaired in some forms of schizophrenia. We conclude that impaired cognitive coordination due to reduced ion flow through NMDA-channels is involved in schizophrenia, and we suggest that it may also be involved in other disorders. This perspective suggests several ways in which further research could enhance our understanding of cognitive coordination, its neural basis, and its relevance to psychopathology.

In search of common foundations for cortical computation

It is worthwhile to search for forms of coding, processing, and learning common to various cortical regions and cognitive functions. Local cortical processors may coordinate their activity by maximizing the transmission of information coherently related to the context in which it occurs, thus forming synchronized population codes. This coordination involves contextual field (CF) connections that link processors within and between cortical regions. The effects of CF connections are distinguished from those mediating receptive field (RF) input; it is shown how CFs can guide both learning and processing without becoming confused with the transmission of RF information. Simulations explore the capabilities of networks built from local processors with both RF and CF connections. Physiological evidence for synchronization, CFs, and plasticity of the RF and CF connections is described. Coordination via CFs is related to perceptual grouping, the effects of context on contrast sensitivity, amblyopia, implicit influences of color in achromotopsia, object and word perception, and the discovery of distal environmental variables and their interactions through self-organization. Cortical computation could thus involve the flexible evaluation of relations between input signals by locally specialized but adaptive processors whose activity is dynamically associated and coordinated within and between regions through specialized contextual connections.

Components of visual memory

Visual recognition memory for a sequence of non-verbalized patterns is shown to have a large and clearly defined recency effect. This recency effect occurs with random list lengths and therefore cannot be due to differential processing of the end items. The effect is completely removed by just 3 s of mental arithmetic but survives for at least 10 s over unfilled intervals. Recognition memory for patterns at other serial positions is slower, less accurate, and shows no primacy effect; performance at these earlier serial positions is dependent upon the time for which patterns are initially presented, but is unaffected by the duration of the retention interval, mental arithmetic, and the time between patterns on initial presentation. These findings provide evidence that visual memory has two components that are closely analogous to the short-term (STM) and long-term (LTM) components of verbal memory. Visual STM, here called visualization, has a capacity of one pattern, cannot be activated LTM, and does not seem to be the gateway to LTM.

Interference with Visualization

It is often claimed that visualizing and perceiving interfere with each other because they compete for special purpose visual processing resources. The arguments for this view (e.g. Brooks, 1967, 1968) are criticised. Five experiments are then reported which attempt to determine whether specific processing activities interfere with the visualization of novel abstract patterns. Visualization was greatly interfered with by adding five digits but not by reading them. Presentation modality of the digits did not affect the interference they caused. When the intervening activity involved processing patterns similar to those being visualized, the amount of interference depended upon whether the subject had to form and use representations that outlived the icon. Perception caused interference when it involved formation of a maintainable representation, but not when it required only sensory storage. It is concluded that visualization requires general purpose resources, and that interference between visualization and perception could be due to competition for these resources.

Function and interaction of on and off transients in vision. II. Neurophysiology.

SummaryNeuronal responses to interruptions of light stimuli were studied in 58 X-type and 7 Y-type LGN relay cells with intra- and extracellular recording techniques. The responses to interruption were then compared with responses to either appearing or disappearing light stimuli which had the same luminance and size as the interrupted stimulus. The extent to which responses to interruption differed from those to appearance and disappearance was studied as a function of the interstimulus interval (ISI), the duration of the stimulus before the interruption (t1) and after the interruption (t2). Responses to stimuli appearing after interruptions of up to 500 msec were weaker than those to appearance and disappearance. This difference decreased with increasing ISI. The difference between responses to appearance and interruption increased as t2 decreased, and decreased as t1 decreased. The reverse was true for the difference between responses to disappearance and interruption. Stimulation of the mesencephalic reticular formation consistently reduced the difference between responses to appearance and disappearance compared with those to interruption for all stimulus conditions.These results are discussed in the context of the psychophysical study presented in the preceding paper. It is shown that the neuronal reactions are reflected in detail by the ability of humans to detect appearances and disappearances that occur during interruptions. EPSP sequences recorded from LGN relay cells and relay cell responses conditioned by reticular stimulation suggest that the differentiation of responses to interruption and change partially occurs already in the retina. This differentiation is subsequently enhanced by antagonistic inhibition in the LGN. It is proposed that these inhibitory interactions at peripheral sites of the visual pathway store visual information and serve to reduce the redundancy of responses to short interruptions of the visual input. Centrifugal modulation of LGN inhibition is proposed to control the trade off between temporal integration and temporal resolution.

Perceptual grouping in disorganized schizophrenia

This study evaluated visual perceptual grouping in schizophrenia to test the hypothesis that the disorganization syndrome in schizophrenia is related to a deficit in cognitive coordination. Perceptual grouping was examined with three psychophysically well-controlled tasks in patients with disorganized schizophrenia (n=11), non-disorganized schizophrenia (n=24), psychotic disorders other than schizophrenia (n=31) and non-psychotic psychiatric disorders (n=35). These measures assessed processing of both concurrent and preceding stimulus context. Deficits in perceptual grouping were observed on all three tasks in disorganized schizophrenia patients. Dysfunctional perceptual grouping mechanisms produced both enhanced and impaired task performance suggesting that the pattern of performance observed was the result of a specific deficit in the grouping of stimulus elements. We interpret these data as further support for the hypothesis that the disorganization syndrome in schizophrenia reflects a widespread deficit in the cognitive coordination of contextually related stimuli, leading to dysfunctional grouping of stimulus features in vision, thought and language.

Function and interaction of on and off transients in vision I. Psychophysics

SummaryPsychophysical experiments were conducted to determine the conditions under which human observers can detect small differences between two successively presented random-dot patterns. The inter-stimulus interval (ISI) varied from 20 to 500 msec. It was found that the appearance of an additional light spot in the second pattern was detectable with ISIs of up to 120 msec. The disappearance of a light spot from the first pattern was detectable with ISIs up to 60 msec. Decreasing the exposure duration of the first pattern worsened the detection of appearance but improved the detection of disappearance. In contrast, decreasing the exposure duration of the second pattern improved the detection of appearance but worsened the detection of disappearance. If the first pattern was presented to one eye and the second pattern to the other under conditions of binocular fusion neither appearance nor disappearance could be detected at any ISI. The results are interpreted as evidence that the transient neural response to the onset of a stimulus is significantly affected by the offset of that stimulus within the preceding 120 msec, and that the transient neural response to the offset of a stimulus is significantly affected by the onset of that stimulus within the following 60 msec. It is suggested that reciprocal inhibition between on- and off-activity could account for these results.

Reaction time and short-term visual memory

Posnefs method of using differences in RT for physical and name matches to estimate the time constant of visual STM is criticized as confounding the decay of the visual trace with the development of a name code. When this confounding is avoided by using stimuli that are hard to name (a 5 by 5 matrix of randomly filled squares), the time constant shown by both RT and errors is consistently longer than that reported by Posner.

Theory of mind and perceptual context-processing in schizophrenia.

Introduction. A series of studies have suggested that schizophrenia patients are deficient in theory of mind (ToM). However, the cognitive mechanisms underlying ToM deficits in schizophrenia are largely unknown. The present study examined the hypothesis that impaired ToM in schizophrenia can be understood as a deficit in context processing. Methods. Disorganised schizophrenia patients (N = 12), nondisorganised schizophrenia patients (N = 36), and nonpsychotic psychiatric patients (N = 26) were tested on three ToM tasks and a visual size perception task, a measure of perceptual context processing. In addition, statistical analyses were carried out which compared chronic, treatment‐refractory schizophrenia patients (N = 28) to those with an episodic course of illness (N = 20). Results. Overall, ToM performance was linked to deficits in context processing in schizophrenia patients. Statistical comparisons showed that disorganised as well as chronic schizophrenia patients were more impaired in ToM but more accurate in a visual size perception task where perceptual context is misleading. Conclusions. This pattern of results is interpreted as indicating a possible link between deficits in ToM and perceptual context processing, which together with deficits in perceptual grouping, are part of a broader dysfunction in cognitive coordination in schizophrenia.