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In the real world, decision making processes must be able to integrate non-stationary information that changes systematically while the decision is in progress. Although theories of decision making have traditionally been applied to paradigms with stationary information, non-stationary stimuli are now of increasing theoretical interest. We use a random-dot motion paradigm along with cognitive modeling to investigate how the decision process is updated when a stimulus changes. Participants viewed a cloud of moving dots, where the motion switched directions midway through some trials, and were asked to determine the direction of motion. Behavioral results revealed a strong delay effect: after presentation of the initial motion direction there is a substantial time delay before the changed motion information is integrated into the decision process. To further investigate the underlying changes in the decision process, we developed a Piecewise Linear Ballistic Accumulator model (PLBA). The PLBA is efficient to simulate, enabling it to be fit to participant choice and response-time distribution data in a hierarchal modeling framework using a non-parametric approximate Bayesian algorithm. Consistent with behavioral results, PLBA fits confirmed the presence of a long delay between presentation and integration of new stimulus information, but did not support increased response caution in reaction to the change. We also found the decision process was not veridical, as symmetric stimulus change had an asymmetric effect on the rate of evidence accumulation. Thus, the perceptual decision process was slow to react to, and underestimated, new contrary motion information.
Copyright © 2015 Elsevier Inc. All rights reserved.
Social impairment is a core feature of schizophrenia, present from the pre-morbid stage and predictive of outcome, but the etiology of this deficit remains poorly understood. Successful and adaptive social interactions depend on one's ability to make rapid and accurate judgments about others in real time. Our surprising ability to form accurate first impressions from brief exposures, known as "thin slices" of behavior has been studied very extensively in healthy participants. We sought to examine affect and social trait judgment from thin slices of static or video stimuli in order to investigate the ability of schizophrenic individuals to form reliable social impressions of others. 21 individuals with schizophrenia (SZ) and 20 matched healthy participants (HC) were asked to identify emotions and social traits for actors in standardized face stimuli as well as brief video clips. Sound was removed from videos to remove all verbal cues. Clinical symptoms in SZ and delusional ideation in both groups were measured. Results showed a general impairment in affect recognition for both types of stimuli in SZ. However, the two groups did not differ in the judgments of trustworthiness, approachability, attractiveness, and intelligence. Interestingly, in SZ, the severity of positive symptoms was correlated with higher ratings of attractiveness, trustworthiness, and approachability. Finally, increased delusional ideation in SZ was associated with a tendency to rate others as more trustworthy, while the opposite was true for HC. These findings suggest that complex social judgments in SZ are affected by symptomatology.
Copyright © 2014 Elsevier B.V. All rights reserved.
Neurons in cortical ventral-stream area V4 are thought to contribute to important aspects of visual processing by integrating information from primary visual cortex (V1). However, how V4 neurons respond to visual stimulation after V1 injury remains unclear: While electrophysiological investigation of V4 neurons during reversible V1 inactivation suggests that virtually all responses are eliminated (Girard et al., 1991), fMRI in humans and monkeys with permanent lesions shows reliable V1-independent activity (Baseler et al., 1999; Goebel et al., 2001; Schmid et al., 2010). To resolve this apparent discrepancy, we longitudinally assessed neuronal functions of macaque area V4 using chronically implanted electrode arrays before and after creating a permanent aspiration lesion in V1. During the month after lesioning, we observed weak yet significant spiking activity in response to stimuli presented to the lesion-affected part of the visual field. These V1-independent responses showed sensitivity for motion and likely reflect the effect of V1-bypassing geniculate input into extrastriate areas.
Self-generated body movements have reliable visual consequences. This predictive association between vision and action likely underlies modulatory effects of action on visual processing. However, it is unknown whether actions can have generative effects on visual perception. We asked whether, in total darkness, self-generated body movements are sufficient to evoke normally concomitant visual perceptions. Using a deceptive experimental design, we discovered that waving one's own hand in front of one's covered eyes can cause visual sensations of motion. Conjecturing that these visual sensations arise from multisensory connectivity, we showed that grapheme-color synesthetes experience substantially stronger kinesthesis-induced visual sensations than nonsynesthetes do. Finally, we found that the perceived vividness of kinesthesis-induced visual sensations predicted participants' ability to smoothly track self-generated hand movements with their eyes in darkness, which indicates that these sensations function like typical retinally driven visual sensations. Evidently, even in the complete absence of external visual input, the brain predicts visual consequences of actions.
Early psychologists, including Galton, Cattell, and Spearman, proposed that intelligence and simple sensory discriminations are constrained by common neural processes, predicting a close link between them. However, strong supporting evidence for this hypothesis remains elusive. Although people with higher intelligence quotients (IQs) are quicker at processing sensory stimuli, these broadly replicated findings explain a relatively modest proportion of variance in IQ. Processing speed alone is, arguably, a poor match for the information processing demands on the neural system. Our brains operate on overwhelming amounts of information, and thus their efficiency is fundamentally constrained by an ability to suppress irrelevant information. Here, we show that individual variability in a simple visual discrimination task that reflects both processing speed and perceptual suppression strongly correlates with IQ. High-IQ individuals, although quick at perceiving small moving objects, exhibit disproportionately large impairments in perceiving motion as stimulus size increases. These findings link intelligence with low-level sensory suppression of large moving patterns--background-like stimuli that are ecologically less relevant. We conjecture that the ability to suppress irrelevant and rapidly process relevant information fundamentally constrains both sensory discriminations and intelligence, providing an information-processing basis for the observed link.
Copyright © 2013 Elsevier Ltd. All rights reserved.
Atypical perceptual processing in autism spectrum disorder (ASD) is well documented. In addition, growing evidence supports the hypothesis that an excitatory/inhibitory neurochemical imbalance might underlie ASD. Here we investigated putative behavioral consequences of the excitatory/inhibitory imbalance in the context of visual motion perception. As stimulus size increases, typical observers exhibit marked impairments in perceiving motion of high-contrast stimuli. This result, termed "spatial suppression," is believed to reflect inhibitory motion-processing mechanisms. Motion processing is also affected by gain control, an inhibitory mechanism that underlies saturation of neural responses at high contrast. Motivated by these behavioral correlates of inhibitory function, we investigated motion perception in human children with ASD (n = 20) and typical development (n = 26). At high contrast, both groups exhibited similar impairments in motion perception with increasing stimulus size, revealing no apparent differences in spatial suppression. However, there was a substantial enhancement of motion perception in ASD: children with ASD exhibited a consistent twofold improvement in perceiving motion. Hypothesizing that this enhancement might indicate abnormal weakening of response gain control, we repeated our measurements at low contrast, where the effects of gain control should be negligible. At low contrast, we indeed found no group differences in motion discrimination thresholds. These low-contrast results, however, revealed weaker spatial suppression in ASD, suggesting the possibility that gain control abnormalities in ASD might have masked spatial suppression differences at high contrast. Overall, we report a pattern of motion perception abnormalities in ASD that includes substantial enhancements at high contrast and is consistent with an underlying excitatory/inhibitory imbalance.
Cross cultural studies have played a pivotal role in elucidating the extent to which behavioral and mental characteristics depend on specific environmental influences. Surprisingly, little field research has been carried out on a fundamentally important perceptual ability, namely the perception of biological motion. In this report, we present details of studies carried out with the help of volunteers from the Mundurucu indigene, a group of people native to Amazonian territories in Brazil. We employed standard biological motion perception tasks inspired by over 30 years of laboratory research, in which observers attempt to decipher the walking direction of point-light (PL) humans and animals. Do our effortless skills at perceiving biological activity from PL animations, as revealed in laboratory settings, generalize to people who have never before seen representational depictions of human and animal activity? The results of our studies provide a clear answer to this important, previously unanswered question. Mundurucu observers readily perceived the coherent, global shape depicted in PL walkers, and experienced the classic inversion effects that are typically found when such stimuli are turned upside down. In addition, their performance was in accord with important recent findings in the literature, in the abundant ease with which they extracted direction information from local motion invariants alone. We conclude that the effortless, veridical perception of PL biological motion is a spontaneous and universal perceptual ability, occurring both inside and outside traditional laboratory environments.
When sensory input allows for multiple, competing perceptual interpretations, observers' perception can fluctuate over time, which is called bistable perception. Imaging studies in humans have revealed transient responses in a right-lateralized network in the frontal-parietal cortex (rFPC) around the time of perceptual transitions between interpretations, potentially reflecting the neural initiation of transitions. We investigated the role of this activity in male human observers, with specific interest in its relation to the temporal structure of transitions, which can be either instantaneous or prolonged by periods during which observers experience a mix of both perceptual interpretations. Using both bistable apparent motion and binocular rivalry, we show that transition-related rFPC activity is larger for transitions that last longer, suggesting that rFPC remains active as long as a transition lasts. We also replicate earlier findings that rFPC activity during binocular rivalry transitions exceeds activity during yoked transitions that are simulated using video replay. However, we show that this established finding holds only when perceptual transitions are replayed as instantaneous events. When replay, instead, depicts transitions with the actual durations reported during rivalry, yoked transitions and genuine rivalry transitions elicit equal activity. Together, our results are consistent with the view that at least a component of rFPC activation during bistable perception reflects a response to perceptual transitions, both real and yoked, rather than their cause. This component of activity could reflect the change in sensory experience and task demand that occurs during transitions, which fits well with the known role of these areas in attention and decision making.
Indirect evidence suggests that the contents of visual working memory may be maintained within sensory areas early in the visual hierarchy. We tested this possibility using a well-studied motion repulsion phenomenon in which perception of one direction of motion is distorted when another direction of motion is viewed simultaneously. We found that observers misperceived the actual direction of motion of a single motion stimulus if, while viewing that stimulus, they were holding a different motion direction in visual working memory. Control experiments showed that none of a variety of alternative explanations could account for this repulsion effect induced by working memory. Our findings provide compelling evidence that visual working memory representations directly interact with the same neural mechanisms as those involved in processing basic sensory events.
Characterizing the temporal limits of the human visual system has long been a central goal of vision research. Spanning three centuries of research, temporal order judgments have been used to estimate the temporal precision of visual processing, with nearly all the research focusing on onset asynchrony discriminations. Recent neurophysiological work, however, demonstrated that neural latencies for stimulus offsets are shorter and less variable than those following event onsets, suggesting that event offsets might provide more reliable timing cues to the visual system than event onsets. Here, we tested this hypothesis by measuring psychophysical thresholds for discriminating onset and offset asynchronies for both stationary and moving stimuli. In three experiments, we showed that offset asynchrony thresholds were indeed consistently lower and were less affected by stimulus variations than onset asynchrony thresholds. These findings are consistent with neurophysiology and suggest a possible role of offset signals as reliable timing references for visual events.
Copyright 2010 Elsevier Ltd. All rights reserved.