Comparable repetition blindness effect in patients with schizophrenia

BACKGROUND AND OBJECTIVES

Repetition blindness (RB) refers to the difficulty to report repetitions of stimuli visually presented in a rapid list. To date only two studies have examined RB in patients with schizophrenia and the results are not clear-cut. The current study was designed to employ a task with reduced memory load, more trials in each experimental condition, and more participants to obtain a more reliable RB effect.

METHODS

A 2x2x3x2 mixed factor repeated measure design was used, with stimulus repetition, lag, and presentation rate as within-subject factors, and group (patient or control) as a between-subject factor. A rapid serial visual presentation (RSVP) procedure was used. Twenty eight inpatients with schizophrenia and 28 healthy controls participated in the experiment.

RESULTS

The patient group showed significantly impaired performance when compared tothe control group in every experimental condition. Nevertheless, the patient group demonstrated similar RB effect as the control group. Furthermore, the overall RB effect observed in patients did not relate to their illness severity or psychotic symptoms. Neither was it related to their age or education.

LIMITATIONS

It was difficult to match the age and education of the control group to that of the inpatient group.

CONCLUSIONS

Patients with schizophrenia performed worse than healthy controls in each experimental condition. Both the control and patient group showed robust RB effect in the short lag with faster rates. In addition, RB effect seemed to be irrelevant to patients' illness severity and clinical symptoms.

The neural basis of temporal individuation and its capacity limits in the human brain

Individuation refers to individuals' use of spatial and temporal properties to register objects as distinct perceptual events relative to other stimuli. Although behavioral studies have examined both spatial and temporal individuation, neuroimaging investigations have been restricted to the spatial domain and at relatively late stages of information processing. Here, we used univariate and multivoxel pattern analyses of functional MRI data to identify brain regions involved in individuating temporally distinct visual items and the neural consequences that arise when this process reaches its capacity limit (repetition blindness, RB). First, we found that regional patterns of blood-oxygen-level-dependent activity across the cortex discriminated between instances where repeated and nonrepeated stimuli were successfully individuated-conditions that placed differential demands on temporal individuation. These results could not be attributed to repetition suppression or other stimulus-related factors, task difficulty, regional activation differences, other capacity-limited processes, or artifacts in the data or analyses. Contrary to current theoretical models, this finding suggests that temporal individuation is supported by a distributed set of brain regions, rather than a single neural correlate. Second, conditions that reflect the capacity limit of individuation-instances of RB-lead to changes in the spatial patterns within this network, as well as amplitude changes in the left hemisphere premotor cortex, superior medial frontal cortex, anterior cingulate cortex, and bilateral parahippocampal place area. These findings could not be attributed to response conflict/ambiguity and likely reflect the core brain regions and mechanisms that underlie the capacity-limited process that gives rise to RB.NEW & NOTEWORTHY We present novel findings into the neural bases of temporal individuation and repetition blindness (RB)-the perceptual deficit that arises when this process reaches its capacity limit. Specifically, we found that temporal individuation is a widely distributed process in the brain and identified a number of candidate brain regions that appear to underpin RB. These findings enhance our understanding of how these fundamental perceptual processes are reflected in the human brain.

The relationship between reversed masked priming and the tri-phasic pattern of the lateralised readiness potential

One of the potential explanations for negative compatibility effects (NCE) in subliminal motor priming tasks has been perceptual prime-target interactions. Here, we investigate whether the characteristic tri-phasic LRP pattern associated with the NCE is caused by these prime-target interactions. We found that both the prime-related phase and the critical reversal phase remain present even on trials where the target is omitted, confirming they are elicited by the prime and mask, not by prime-target interactions. We also report that shape and size of the reversal phase are associated with response speed, consistent with a causal role for the reversal for the subsequent response latency. Additionally, we analysed sequential modulation of the NCE by previous conflicting events, even though such conflict is subliminal. In accordance with previous literature, this modulation is small but significant.

The neural basis of temporal individuation and its capacity limits in the human brain

Individuation refers to individuals' use of spatial and temporal properties to register an object as a distinct perceptual event relative to other stimuli. Although behavioral studies have examined both spatial and temporal individuation, neuroimaging investigations of individuation have been restricted to the spatial domain and at relatively late stages of information processing. In this study we used univariate and multivoxel pattern analyses of functional magnetic resonance imaging data to identify brain regions involved in individuating temporally distinct visual items and the neural consequences that arise when this process reaches its capacity limit (repetition blindness, RB). First, we found that regional patterns of blood oxygen level-dependent activity in a large group of brain regions involved in "lower-level" perceptual and "higher-level" attentional/executive processing discriminated between instances where repeated and nonrepeated stimuli were successfully individuated, conditions that placed differential demands on temporal individuation. These results could not be attributed to repetition suppression, stimulus or response factors, task difficulty, regional activation differences, other capacity-limited processes, or artifacts in the data or analyses. Consistent with the global workplace model of consciousness, this finding suggests that temporal individuation is supported by a distributed set of brain regions, rather than a single neural correlate. Second, conditions that reflect the capacity limit of individuation (instances of RB) modulated the amplitude, rather than spatial pattern, of activity in the left hemisphere premotor cortex. This finding could not be attributed to response conflict/ambiguity and likely reflects a candidate brain region underlying the capacity-limited process that gives rise to RB.

Repetition blindness is immune to the central bottleneck

The attentional blink (AB) and repetition blindness (RB) phenomena refer to subjects' impaired ability to detect the second of two different (AB) or identical (RB) target stimuli in a rapid serial visual presentation stream if they appear within 500 msec of one another. Despite the fact that the AB reveals a failure of conscious visual perception, it is at least partly due to limitations at central stages of information processing. Do all attentional limits to conscious perception have their locus at this central bottleneck? To address this question, here we investigated whether RB is affected by online response selection, a cognitive operation that requires central processing. The results indicate that, unlike the AB, RB does not result from central resource limitations. Evidently, temporal attentional limits to conscious perception can occur at multiple stages of information processing.

Comparison of event-related potentials in attentional blink and repetition blindness

Attending to the first target in rapid serial visual presentation (RSVP) interferes with processing of the second target so that the participants fail to recognize the second target if the targets are separated by a stimulus onset asynchrony of 200-500 ms. This phenomenon is attentional blink (AB). Repetition blindness (RB) is an additional difficulty to recognize the second occurrence of the same stimulus in RSVP. A controversial issue in studies of both deficits is the processing level at which they occur. To compare the timing and mechanisms of AB and RB directly during the same RSVP stream, we recorded event-related potentials (ERPs) in response to repeated and unrepeated targets. Comparable to earlier ERP studies on visual awareness, the results showed for both types of targets a negative amplitude difference between ERPs to consciously recognized and unrecognized targets during 250-350 ms from stimulus onset, suggesting that both AB and RB are associated with deficits of conscious perception, occurring at earlier stages than access to working memory. However, the perceptual deficit in RB is more severe, which may be related to higher overall negativity in response to repeated targets observed 150-300 ms after stimulus onset, suggesting stronger cortical baseline activation and higher perceptual threshold for repeated targets as compared with unrepeated ones.

When do irrelevant visual stimuli impair processing of identical targets?

Three experiments investigated whether the repeated-letter inferiority effect (RLIE) and repetition blindness (RB) are identical phenomena or not and how the RLIE can be reconciled with the flanker compatibility effect (FCE). Participants reported a masked target and ignored an unmasked distractor. We manipulated the type of distractor (identical, alternative target, or neutral), the order of presenting distractor and target, and the predictability of target location. When distractors preceded the targets, distractors identical to the target always caused deficits in target processing (i.e., RB). With simultaneous presentation, identical distractors caused deficits (i.e., an RLIE) for unpredictable target locations only. Yet the RLIE was significantly smaller than RB. This result suggests that simultaneously presented stimuli are identified serially, in random order, if target position is unpredictable. As a result, RB arises only in the 50% of all trials with identical distractors in which the distractor is identified before the target. With simultaneous presentation and predictable target location, however, parallel processing of targets and distractors was possible that gave rise to an FCE in recognition accuracy. Analyses of false alarm rates revealed no evidence of significant response biases.

Repetition blindness in rapid lists: activation and inhibition versus construction and attribution

The authors examine the repetition blindness effect--the failure to report one of the occurrences of a word presented twice in a rapid list. This phenomenon has been ascribed to inhibitory processes that prevent immediate tokenization of the 2nd occurrence of a repeated word. The authors present several kinds of evidence against that account, including observations that repetition blindness (a) does not occur when repetitions are not embedded in a list of familiar orthographic units, (b) is alleviated by precuing the subject with the identity of the word that may repeat within a rapid list, and (c) can be caused by cues presented after the list, when the opportunity for inhibition has passed. It is proposed that repetition blindness can better be understood through the principles of construction and attribution.

When words collide: facilitation and interference in the report of repeated words from rapidly presented lists

Inhibited encoding is the basis of some accounts of repetition blindness--impaired report of the second occurrence of a repeated word in a rapidly presented word sequence. The author presents evidence for the claim that repetition effects arise from constructive processes of perception and memory that occur to some extent after the word sequence has been presented. Unpredictable postlist cues prompted subjects to report either the entire list or just the final word in the list. Repetition impaired the report of the second occurrence of a repeated word under full report but facilitated the report of such items when only the final word had to be reported. The author modulated this dissociation by presenting repeated words in sentences rather than unrelated word lists. The sensitivity of the effects of repetition to postlist cues supports a construction rather than an encoding inhibition account of repetition blindness.

Repetition Blindness: Out of Sight or Out of Mind?

Does repetition blindness represent a failure of perception or of memory? In Experiment 1, participants viewed rapid serial visual presentation (RSVP) sentences. When critical words (C1 and C2) were orthographically similar, C2 was frequently omitted from serial report; however, repetition priming for C2 on a postsentence lexical decision task was equivalent whether or not C1 was similar to C2. In Experiment 2, participants monitored RSVP sentences for a predetermined target. Participants frequently failed to detect the target when it was preceded by an orthographically similar word. In Experiment 3, the authors investigated the role of the attentional blink in this effect. These experiments suggest that repetition blindness is a failure of conscious perception, consistent with predictions of the token-individuation hypothesis.

Repetition blindness for words yet repetition advantage for nonwords

Accuracy of report of words in a rapidly presented sequence is reduced if 1 word is a repetition of a previous word. This is repetition blindness. If, however, the items are pronounceable nonwords, or pseudohomophones, repetition improves recall. A repetition advantage for nonwords also occurs when subjects merely count the items or when the item between the critical nonwords is a familiar word. Familiarizing subjects with the nonwords improved the level of recall but did not affect the repetition advantage. These results are considered in relation to token individuation and other accounts of repetition blindness. The findings suggest that for identical linguistic stimuli the types bound to episodic memory tokens that are vulnerable to repetition blindness are lexical units.