Stimulus frequency influences spontaneous perceptual reversals in ambiguous apparent motion

The temporal integration of continuous sensory information into a temporally extended percept becomes evident in spontaneous reversals of ambiguous apparent motion. To study the temporal relation of spontaneous percept reversals and temporal stimulus properties, we systematically varied presentation frequency in an ambiguous-apparent-motion paradigm. Moreover, we triggered percept reversals in a manner that was not consciously perceived by manipulating the duration of single frames. We found that the reversal rate depended on the stimulus frequency (with higher frequencies resulting in faster percept reversals) and that we could externally trigger perceptual reversals. Our findings support the idea that spontaneous reversals of ambiguous apparent motion are influenced by bottom-up effects at early processing levels. The paradigm allows for specific contrasts of spontaneous and externally triggered (but otherwise identical) perceptual reversals and, by this means, for further study of the underlying mechanisms.     

视知觉学习的认知与神经机制研究

知觉学习是指由于训练或经验而引起的长期稳定的知觉变化,是一种内隐性的学习。近20年来,视知觉学习的大量研究结果提示大脑皮层的各个区域,甚至包括初级感觉皮层,在成熟之后仍然具有一定的可塑性。该文根据近年来的研究进展,对视知觉学习在大脑的什么地方,什么时候,以何种方式发生等热点问题进行了探讨。研究提示,视知觉学习涉及了包括初级视皮层在内的多个大脑皮层,并且存在一种自上而下的调控机制;视知觉学习可以在不同的时间尺度上发生,快速学习之后将伴随着慢速学习;通过视知觉学习,人们对于复杂物体的表征将从高级皮层区域移向低级皮层区域,任务执行也将趋于自动化     

The involvement of central attention in visual search is determined by task demands

Attention, the mechanism by which a subset of sensory inputs is prioritized over others, operates at multiple processing stages. Specifically, attention enhances weak sensory signal at the perceptual stage, while it serves to select appropriate responses or consolidate sensory representations into short-term memory at the central stage. This study investigated the independence and interaction between perceptual and central attention. To do so, I used a dual-task paradigm, pairing a four-alternative choice task with a visual search task. The results showed that central attention for response selection was engaged in perceptual processing for visual search when the number of search items increased, thereby increasing the demand for serial allocation of focal attention. By contrast, central attention and perceptual attention remained independent as far as the demand for serial shifting of focal attention remained constant; decreasing stimulus contrast or increasing the set size of a parallel search did not evoke the involvement of central attention in visual search. These results suggest that the nature of concurrent visual search process plays a crucial role in the functional interaction between two different types of attention.     

Reversal negativity and bistable stimuli: Attention,awareness, or something else?

Ambiguous (or bistable) figures are visual stimuli that have two mutually exclusive perceptual interpretations that spontaneously alternate with each other. Perceptual reversals, as compared with non-reversals, typically elicit a negative difference called reversal negativity (RN), peaking around 250 ms from stimulus onset. The cognitive interpretation of RN remains unclear: it may reflect either bottom-up processes, attentional processes that select between the alternative views of the stimulus, or it may reflect the change in the contents of subjective awareness. In the present study, event-related potentials in response to endogenous unilateral and bilateral reversals of two Necker lattices were compared with exogenously induced reversals of unambiguous lattices. The RN neither resembled the attention-related N2pc response, nor did it correlate with the content of subjective visual awareness. Thus, we conclude that RN is a non-attentional ERP correlate of the changes in the perceptual configuration of the presented object.     

The Neural Basis of Selective Attention: Cortical Sources and Targets of Attentional Modulation

ABSTRACT— Selective attention is an intrinsic component of perceptual representation in a visual system that is hierarchically organized. Modulatory signals originate in brain regions that represent behavioral goals; these signals specify which perceptual objects are to be represented by sensory neurons that are subject to contextual modulation. Attention can be deployed to spatial locations, features, or objects, and corresponding modulatory signals must be targeted within these domains. Open questions include how nonspatial perceptual domains are modulated by attention and how abstract goals are transformed into targeted modulatory signals.     

Distinct and common cortical activations for multimodal semantic categories

If semantic representations are based on particular types of perceptual features, then category knowledge that arises from multimodal sensory experiences should rely on distinct and common sensory brain regions depending on the features involved. Using a similarity-based generation-andcomparison task, we found that semantic categories activated cortical areas associated with taste and smell, biological motion, and visual processing. Fruit names specifically activated medial orbitofrontal regions associated with taste and smell. Labels for body parts and clothing activated lateral temporal occipitoparietal areas associated with perceiving the human body. More generally, visually biased categories activated ventral temporal regions typically ascribed to visual object recognition, whereas functional categories activated lateral frontotemporal areas previously associated with the representation of usage properties. These results indicate that semantic categories that are distinguished by particular perceptual properties rely on distinct cortical regions, whereas semantic categories that rely on similar types of features depend on common brain areas.     

Self-stimulatory behavior and perceptual reinforcement.

Self-stimulatory behavior is repetitive, stereotyped, functionally autonomous behavior seen in both normal and developmentally disabled populations, yet no satisfactory theory of its development and major characteristics has previously been offered. We present here a detailed hypothesis of the acquisition and maintenance of self-stimulatory behavior, proposing that the behaviors are operant responses whose reinforcers are automatically produced interoceptive and exteroceptive perceptual consequences. The concept of perceptual stimuli and reinforcers, the durability of self-stimulatory behaviors, the sensory extinction effect, the inverse relationship between self-stimulatory and other behaviors, the blocking effect of self-stimulatory behavior on new learning, and response substitution effects are discussed in terms of the hypothesis. Support for the hypothesis from the areas of sensory reinforcement and sensory deprivation is also reviewed. Limitations of major alternative theories are discussed, along with implications of the perceptual reinforcement hypothesis for the treatment of excessive self-stimulatory behavior and for theoretical conceptualizations of functionally related normal and pathological behaviors.     

Binocular rivalry alternation rate declines with age

The effect of aging on the time of spontaneous perceptual alternation in binocular rivalry was examined in 59 subjects. An earlier study reported the change of alternation time by comparing middle-age and elderly subjects. We also observed age-related prolongation in alternation time by comparing subjects in a lower age group (20-34 years) with those in both a middle-age group (35-49 years) and a higher age group (50-64 years). Aging of visual optical functions such as presbyopia or the reduction of contrast sensitivity has an accelerating effect over age and may not be related to the age-associated monotonic prolongation of alternation time in binocular rivalry. The origin of aging in binocular rivalry is still unclear but a neural interval generator for perceptual switching is suggested.     

Shifting spatial attention makes you flip: Exogenous visual attention triggers perceptual alternations during binocular rivalry

Although it has been argued that visual attention and the dynamics of binocular rivalry are closely linked, strong evidence for this proposition is still lacking. Here, we investigate how perceptual alternations during binocular rivalry are affected by spatial attention by employing a cuing paradigm. We show a tight link between the occurrence of perceptual alternations and the spatiotemporal properties of visual attention: Alternations occurred earlier and more frequently at locations where visual attention was summoned by an exogenous cue. We argue that cuing a location where rival images are presented leads to a transient increase in the effective contrast of these rival images. This transient increase in effective contrast increases the probability of an alternation at that location. Furthermore, we suggest that an occipito-fronto-parietal network known to be involved in selective attention and binocular rivalry mediates perceptual alternations by boosting the neural response at attended locations.     

Attentional spread in deaf and hearing participants: Face and object distractor processing under perceptual load

The case of human deafness constitutes a unique opportunity to examine possible consequences for perceptual processing due to altered sensory experiences. We tested whether deaf??in contrast to hearing??individuals are more susceptible to visual distraction from peripheral than from central face versus object stimuli. The participants were required to classify the gender of a target male or female symbol presented either alone (low perceptual load) or together with three filler symbols (high perceptual load), while ignoring gender-congruent or -incongruent face versus object distractors presented at central or peripheral positions. The gender classifications were affected by distractor gender under low, but not under high, perceptual load in hearing participants. In contrast, the responses of deaf participants were similarly influenced by distractor gender under both levels of perceptual load. There was no evidence for generally enhanced attention to the visual periphery in deaf individuals. Our results indicate that auditory deprivation may result in enhanced attentional capacities under high perceptual load.     

大脑视知觉调控的神经机制

大脑的知觉加工并非单纯由外部刺激驱动,而是存在自上而下的知觉调控。尽管这一现象被大量实验研究证实,但其神经机制仍然是认知神经科学研究的重要问题。本研究系统介绍了知觉调控的神经基础、实现形式、研究范式,及其理论模型,分析指出了当前研究面临的主要问题,并对未来的研究进行了展望,以期促进该问题研究的进一步开展。     

Symbolic magnitude modulates perceptual strength in binocular rivalry

Basic aspects of magnitude (such as luminance contrast) are directly represented by sensory representations in early visual areas. However, it is unclear how symbolic magnitudes (such as Arabic numerals) are represented in the brain. Here we show that symbolic magnitude affects binocular rivalry: perceptual dominance of numbers and objects of known size increases with their magnitude. Importantly, variations in symbolic magnitude acted like variations in luminance contrast: we found that an increase in numerical magnitude of adding one lead to an equivalent increase in perceptual dominance as a contrast increment of 0.32%. Our results support the claim that magnitude is extracted automatically, since the increase in perceptual dominance came about in the absence of a magnitude-related task. Our findings show that symbolic, acculturated knowledge about magnitude interacts with visual perception and affects perception in a manner similar to lower-level aspects of magnitude such as luminance contrast.     

A general mechanism for decision-making in the human brain?

A new fMRI study by Heekeren and colleagues suggests that left dorsolateral prefrontal cortex (DLPFC) contains a region that integrates sensory evidence supporting perceptual decisions. DLPFC meets two criteria posited by Heekeren et al. for such a region: (1) its activity is correlated in time with the output of sensory areas of the visual cortex measured simultaneously, and (2) as expected of an integrator, its activity is greater on trials for which the sensory evidence is substantial than on trials for which the sensory evidence is weak. Complementary experiments in humans and monkeys now offer a realistic hope of elucidating decision-making networks in the primate brain.     

Neural correlates of age-related reduction in visual motion priming

Previously we reported that priming of visual motion perception is reduced in older adults compared to younger adults (Jiang, Greenwood, & Parasuraman, 1999, Psychology and Aging, 14(4), 619; Jiang, Luo, & Parasuraman, 2002b, Neuropsychology, 16(2), 140). To examine the neural mechanisms underlying this age-related effect, event-related brain potentials (ERPs) were recorded during perceptual judgments of motion directions by younger and older adults in two experiments. When judging single-step motion, both younger and older adults evoked significantly larger ERP late positive component (LPC) responses to unambiguous motion compared to LPC responses elicited by ambiguous motion. In contrast, compared to the younger adults, the older adults evoked comparable but delayed ERP responses to single motion steps. In the second experiment the younger and older groups judged the directions of two successive motion-steps (either motion priming or motion reversals). Under short (200-400 ms) stimulus onset asynchrony (SOA), the difference between the ERP responses to priming and reversal conditions was significantly larger for the younger than for the older adults. This study provides the first electrophysiological evidence that brain aging leads to delayed processing of single motion direction and visual motion priming as early as 100 ms in the early visual cortex. Age-related changes in strength and temporal characteristics of neural responses in temporal-parietal regions were particularly pronounced in older adults when successive motion signals are placed closely in time, within 400 ms.     

Early top-down influences on bistable perception revealed by event-related potentials

A longstanding debate exists in the literature concerning bottom-up vs. top-down influences on bistable perception. Recently, a technique has been developed to measure early changes in brain activity (via ERPs) related to perceptual reversals (Kornmeier & Bach, 2004). An ERP component, the reversal negativity (RN) has been identified, and is characterized as an increase in negative potential over the posterior scalp from 150 to 350 ms for perceptual reversals compared to perceptual stability. This finding, although interesting, has not helped resolve issues related to the bottom-up vs. top-down debate because top-down influences have not been directly manipulated. The current study focused on resolving some of these issues by measuring the RN while observers maintained one of three 'intentional approaches', (1) try to reverse perception as often as possible, (2) try to stabilize perception for as long as possible, and (3) maintain a passive approach. Enhancements in RN amplitude were found for the intention-to-reverse condition compared to the passive condition. This finding suggests an early influence (150 ms) of top-down control on perceptual reversals of bistable figures. Results are discussed in terms of competing attention shifting vs. fatigue-based theories of bistable perception.     

Implicit learning modulates selective attention at sensory levels of perceptual processing

Electrophysiological evidence suggests that attention can be modulated as early as 100 msec after stimulus presentation. However, it is not clear whether these changes are based primarily on stimulus properties such as perceptual load (i.e., the level of perceptual difficulty), or other properties, such as general attentional set or learned expectations concerning perceptual load. Using event-related potentials, this study examined how implicit learning of perceptual load conditions modulates selective attention at sensory levels of perceptual analysis. The results show significant differences in P1 amplitude recorded over occipital areas of the brain as a function of learned expectations of perceptual load, only when perceptual load could be reliably predicted by the preceding stimuli. Moreover, differences in processing were found when both low and high perceptual load conditions could be predicted. These findings suggest that implicit learning modulates the allocation of attention at early stages of perceptual processing.     

How visual imagery interferes with vision.

Mental visual imagery interferes with vision: the Perky (1910) effect. Is the effect optical, sensory, perceptual, attentional, or just a response bias? Acuity was measured (in undergraduates and graduates) using target lines, with and without images (of lines). Optics (fixation, pupil size, accommodation), response bias, global attention (effort; diversion of attention to imagery), perceptual assimilation (target incorporation by imagery) and perceptual masking (of target by imagery) all fail to explain the effect. Foveally, local attention plays a limited role, as the Perky effect in divided attention is half that in focused attention, but this interaction vanishes with extrafoveal targets. Images produce primarily sensory interference, mimicking a reduction in target energy.     

Electrophysiological and phenomenological effects of short-term immersion in an altered sensory environment

We examined the spontaneous cerebral electrophysiology and phenomenology during short-term perceptual deprivation consisting of an edgeless visual field combined with monotonous auditory input that eliminated potential grounding cues (multimodal Ganzfeld). Subjects (N = 22) were instructed to self-report perceptual fading using a button press. Relaxed wakefulness with closed eyes and viewing of a time-varying stimulus array served as control conditions. The power of parieto-occipital alpha rhythms during perceptual deprivation was midway between the eyes-closed and eyes-open conditions, with a state-specific frequency acceleration. Oscillatory alpha power remained enhanced in the multimodal Ganzfeld relative to viewing time-varying signals, despite no indication of diminished brain arousal. Subjects experienced a range of perceptual phenomena while in the altered sensory environment and individuals with faster alpha oscillations self-reported a greater number of fading episodes. We suggest that alpha-band electroencephalogram (EEG) dynamics signal internally oriented mentation in response to brief perceptual deprivation.     

Perceptual flexibility is coupled with reduced executive inhibition in students of the visual arts

Artists often report that seeing familiar stimuli in novel and interesting ways plays a role in visual art creation. However, the attentional mechanisms which underpin this ability have yet to be fully investigated. More specifically, it is unclear whether the ability to reinterpret visual stimuli in novel and interesting ways is facilitated by endogenously generated switches of attention, and whether it is linked in turn to executive functions such as inhibition and response switching. To address this issue, the current study explored ambiguous figure reversal and executive function in a sample of undergraduate students studying arts and non-art subjects (N = 141). Art students showed more frequent perceptual reversals in an ambiguous figure task, both when viewing the stimulus passively and when eliciting perceptual reversals voluntarily, but showed no difference from non-art students when asked to actively maintain specific percepts. In addition, art students were worse than non-art students at inhibiting distracting flankers in an executive inhibition task. The findings suggest that art students can elicit endogenous shifts of attention more easily than non-art students but that this faculty is not directly associated with enhanced executive function. It is proposed that the signature of artistic skill may be increased perceptual flexibility accompanied by reduced cognitive inhibition; however, future research will be necessary to determine which particular subskills in the visual arts are linked to aspects of perception and executive function.     

Vision merges with touch in a purely tactile discrimination

To construct a coherent percept of the world, the brain continuously combines information across multiple sensory modalities. Simple stimuli from different modalities are usually assumed to be processed in distinct brain areas. However, there is growing evidence that simultaneous stimulation of multiple modalities can influence the activity in unimodal sensory areas and improve or impair performance in unimodal tasks. Do these effects reflect a genuine cross-modal integration of sensory signals, or are they due to changes in the perceiver's ability to locate the stimulus in time and space? We used a behavioral measure to differentiate between these explanations. Our results demonstrate that, under certain circumstances, a noninformative flash of light can have facilitative or detrimental effects on a simple tactile discrimination. The effect of the visual flash mimics that produced by a constant tactile pedestal stimulus. These findings reveal that sensory signals from different modalities can be integrated, even for perceptual judgments within a single modality.