Evidence for perceptual "trapping" and adaptation in multistable binocular rivalry

When a different pattern is presented to each eye, the perceived image spontaneously alternates between the two patterns (binocular rivalry); the dynamics of these bistable alternations are known to be stochastic. Examining multistable binocular rivalry (involving four dominant percepts), we demonstrated path dependence and on-line adaptation, which were equivalent whether perceived patterns were formed by single-eye dominance or by mixed-eye dominance. The spontaneous perceptual transitions tended to get trapped within a pair of related global patterns (e.g., opponent shapes and symmetric patterns), and during such trapping, the probability of returning to the repeatedly experienced patterns gradually decreased (postselection pattern adaptation). These results suggest that the structure of global shape coding and its adaptation play a critical role in directing spontaneous alternations of visual awareness in perceptual multistability.     

Reconstructing the world: switching from segmentation to integration allows neurons in area MT to make "sense" of the visual scene

Huang et al. in this issue of Neuron show that primate area MT neurons exploit contextual cues to adequately interpret motion information. MT neurons switch from segmentation to integration when motion arises from single rather than multiple objects. This switching may help solve the aperture problem and bind distant object components into a perceptual whole.     

Audiovisual integration: an investigation of the "streaming-bouncing" phenomenon

Temporal aspects of the perceptual integration of audiovisual information were investigated by utilizing the visual "streaming-bouncing" phenomenon. When two identical visual objects move towards each other, coincide, and then move away from each other, the objects can either be seen as streaming past one another or bouncing off each other. Although the streaming percept is dominant, the bouncing percept can be induced by presenting an auditory stimulus during the visual coincidence of the moving objects. Here we show that the bounce-inducing effect of the auditory stimulus is paramount when its onset and offset occur in temporal proximity of the onset and offset of the period of visual coincidence of the moving objects. When the duration of the auditory stimulus exceeded this period, visual bouncing disappears. Implications for a temporal window of audiovisual integration and the design of effective audiovisual warning signals are discussed.     

The visual perceptual range of a lizard, <Emphasis Type="Italic">Tiliqua rugosa</Emphasis>

The fragmentation of landscapes produces habitat gaps where the distance between visual landmarks may exceed the perceptual range of a species and impose navigational constraints. We estimated the visual perceptual range of the Australian sleepy lizard, Tiliqua rugosa, by releasing individuals in the centre of a cleared arena in high temperature conditions, with a 0.5-m-high bush placed either 10, 20 or 30 m from the release site. Lizards were more likely to locate those bushes and shelter under them when they were closer, and no lizards found a bush at 30 m. In addition, lizards were less likely to move from the release point when bushes were at 30 m than when they were at the two closer distances. These data suggest that for sleepy lizards the perceptual range for a 0.5-m-high bush is about 20 m. In the uncleared chenopod shrub-land where these lizards live, suitable shelter bushes are an average of 10.5 m from any point in their home range, well within their perceptual range.     

Neuronal activity and its links with the perception of multi-stable figures

In order to isolate the neuronal activity that relates to the making of perceptual decisions, we have made use of a perceptually ambiguous motion stimulus. This stimulus lies on the boundary between two perceptual categories that correspond to clockwise and counter-clockwise rotation of a three-dimensional figure. It consists of a two-dimensional pattern of moving dots that are capable of generating these two, distinct, three-dimensional percepts. We have studied the responses of neurons in cortical area V5/MT whilst macaque monkeys report judgements about the perceptual configuration of this stimulus. We extract a quantitative statistic called 'choice probability' that expresses the covariation of neuronal activity and perceptual choice. An analysis of choice probabilities shows that the pool of neurons involved in the perceptual decisions is a tightly constrained subset of the population of sensory neurons relevant to the perceptual task.     

Dichromatic color language: "reds" and "greens" don't look alike but their colors do.

When protanopes or deuteranopes arrange the Farnsworth Dichotomous Test colors in order of similarity, they reveal their lack of red/green hue discriminations by alternating chips that the normal trichromat sees as reddish and greenish test colors. The dichromatic orderings follow a systematic variation in saturation of blue hues through neutral and into yellow hues as described by theory for each of the two types. Some dichromats who show the typical test behavior nevertheless use reddish and greenish hue terms appropriately when instructed to name the same test colors. Lightness cues are probably used by these dichromats in the naming task but ignored in the perceptual similarity task. Thus, unlike normal trichromats, who use similar names for perceptually similar colors, dichromats may use dissimilar names for perceptually similar colors. In this way they can achieve concordance with the normative language system despite its discordance with their impoverished color perceptions.     

Perceptuo-motor interactions in the perceptual organization of speech: evidence from the verbal transformation effect

The verbal transformation effect (VTE) refers to perceptual switches while listening to a speech sound repeated rapidly and continuously. It is a specific case of perceptual multistability providing a rich paradigm for studying the processes underlying the perceptual organization of speech. While the VTE has been mainly considered as a purely auditory effect, this paper presents a review of recent behavioural and neuroimaging studies investigating the role of perceptuo-motor interactions in the effect. Behavioural data show that articulatory constraints and visual information from the speaker's articulatory gestures can influence verbal transformations. In line with these data, functional magnetic resonance imaging and intracranial electroencephalography studies demonstrate that articulatory-based representations play a key role in the emergence and the stabilization of speech percepts during a verbal transformation task. Overall, these results suggest that perceptuo (multisensory)-motor processes are involved in the perceptual organization of speech and the formation of speech perceptual objects.     

Some mistakes go unpunished: the evolution of "all or nothing" signalling

Many models of honest signaling, based on Zahavi's handicap principle, predict that if receivers are interested in a quality that shows continuous variation across the population of signalers, then the distribution of signal intensities will also be continuous. However, it has previously been noted that this prediction does not agree with empirical observation in many signaling systems, where signals are limited to a small number of levels despite continuous variation in the trait being signaled. Typically, there is a critical value of the trait, with all individuals with trait values on one side of the threshold using the same cheap signal, and all those with trait values on the other side of the threshold using the same expensive signal. It has already been demonstrated that these classical models naturally predict such "all-or-nothing signaling" if it is additionally assumed that receivers suffer from perceptual error in evaluating signal strength. We show that such all-or-nothing signaling is also predicted if receivers are limited to responding to the signals in one of two ways. We suggest that many ecological situations (such as the decision to attack the signaler or not, or mate with the signaler or not) involve such binary choices.     

The Importance of Perceptual Experience in the Esthetic Appreciation of the Body

Several studies suggest that sociocultural models conveying extreme thinness as the widespread ideal of beauty exert an important influence on the perceptual and emotional representation of body image. The psychological mechanisms underlying such environmental influences, however, are unclear. Here, we utilized a perceptual adaptation paradigm to investigate how perceptual experience modulates body esthetic appreciation. We found that the liking judgments of round bodies increased or decreased after brief exposure to round or thin bodies, respectively. No change occurred in the liking judgments of thin bodies. The results suggest that perceptual experience may shape our esthetic appreciation to favor more familiar round body figures. Importantly, individuals with more deficits in interoceptive awareness were less prone to increase their liking ratings of round bodies after exposure, suggesting a specific risk factor for the susceptibility to the influence of the extreme thin vs. round body ideals of beauty portrayed by the media.     

Blinded by the load: attention,awareness and the role of perceptual load

What is the relationship between attention and conscious awareness? Awareness sometimes appears to be restricted to the contents of focused attention, yet at other times irrelevant distractors will dominate awareness. This contradictory relationship has also been reflected in an abundance of discrepant research findings leading to an enduring controversy in cognitive psychology. Lavie''s load theory of attention suggests that the puzzle can be solved by considering the role of perceptual load. Although distractors will intrude upon awareness in conditions of low load, awareness will be restricted to the content of focused attention when the attended information involves high perceptual load. Here, we review recent evidence for this proposal with an emphasis on the various subjective blindness phenomena, and their neural correlates, induced by conditions of high perceptual load. We also present novel findings that clarify the role of attention in the response to stimulus contrast. Overall, this article demonstrates a critical role for perceptual load across the spectrum of perceptual processes leading to awareness, from the very early sensory responses related to contrast detection to explicit recognition of semantic content.     

Improving the performance of the amblyopic visual system

Experience-dependent plasticity is closely linked with the development of sensory function; however, there is also growing evidence for plasticity in the adult visual system. This review re-examines the notion of a sensitive period for the treatment of amblyopia in the light of recent experimental and clinical evidence for neural plasticity. One recently proposed method for improving the effectiveness and efficiency of treatment that has received considerable attention is ‘perceptual learning’. Specifically, both children and adults with amblyopia can improve their perceptual performance through extensive practice on a challenging visual task. The results suggest that perceptual learning may be effective in improving a range of visual performance and, importantly, the improvements may transfer to visual acuity. Recent studies have sought to explore the limits and time course of perceptual learning as an adjunct to occlusion and to investigate the neural mechanisms underlying the visual improvement. These findings, along with the results of new clinical trials, suggest that it might be time to reconsider our notions about neural plasticity in amblyopia.     

Involvement of the visual change detection process in facilitating perceptual alternation in the bistable image

A bistable image induces one of two perceptual alternatives. When the bistable visual image is continuously viewed, the percept of the image alternates from one possible percept to the other. Perceptual alternation was previously reported to be induced by an exogenous perturbation in the bistable image, and this perturbation was theoretically interpreted to cause neural noise, prompting a transition between two stable perceptual states. However, little is known experimentally about the visual processing of exogenously driven perceptual alternation. Based on the findings of a previous behavioral study (Urakawa et al. in Perception 45:474–482, 2016), the present study hypothesized that the automatic visual change detection process, which is relevant to the detection of a visual change in a sequence of visual events, has an enhancing effect on the induction of perceptual alternation, similar to neural noise. In order to clarify this issue, we developed a novel experimental paradigm in which visual mismatch negativity (vMMN), an electroencephalographic brain response that reflects visual change detection, was evoked while participants continuously viewed the bistable image. In terms of inter-individual differences in neural and behavioral data, we found that enhancements in the peak amplitude of vMMN1, early vMMN at a latency of approximately 150 ms, correlated with increases in the proportion of perceptual alternation across participants. Our results indicate the involvement of automatic visual change detection in the induction of perceptual alternation, similar to neural noise, thereby providing a deeper insight into the neural mechanisms underlying exogenously driven perceptual alternation in the bistable image.     

Independent psychophysical measurement of experimental modulations in the somatotopy of cutaneous heat-pain stimuli

Distortions of the body image have been repeatedly reported for various clinical conditions, but direct experimental analyses of the perceptual changes involved are still scarce. In addition, most experimental studies rely on cerebral activation patterns to assess neuroplastic changes in central representation, although the relationship between cerebral topography and the topology of the perceptual space is not clear. This study examines whether the direct psychophysical mapping approach we introduced recently (Trojan et al., Brain Res 2006;1120:106–113) is capable of tracking perceptual distortions in the somatotopic representation of heat-pain stimuli. Eleven healthy participants indicated the perceived positions of CO₂ laser stimuli, repetitively presented to the dorsal forearm, with a 3D tracking system in two consecutive sessions, separated by the topical application of capsaicin cream. In line with earlier reports, we expected that the resulting individual perceptual maps (i.e., one-dimensional projections of the perceived positions onto the forearm surface) would be subject to modulation through the altered sensory input, to be measured in terms of altered topological parameters. We found that the topology and metrics of the somatotopic representation were well preserved in the second session, but that the perceptual map was compressed to a smaller range in 9 out of 11 participants. By providing dimensional measures of perceptual representations, perceptual maps constitute an independent, genuinely psychological complement to the topography of cortical activations measured with neuroimaging methods. In addition, we expect them to be useful in diagnosing pathological changes in body perception accompanying chronic pain and other disorders.     

Factors contributing to the integration of textural qualities: Evidence from virtual surfaces

Two experiments involving indirect touch were carried out to explore the relationships among perceptual dimensions of haptically examined surfaces. Subjects in both experiments used a stylus to evaluate the properties of virtual surfaces created by a force-feedback device; four surface properties (resistance to normal force, coefficient of friction, texture scale, and vibration amplitude) were manipulated in various combinations. In Experiment 1, the extent to which there was a one-to-one relationship between specific stimulus properties and perceptual qualities (“perceptual separability”) was evaluated. A substantial failure of separability was demonstrated, with friction tending to be more separable from the other properties than they were from one another. The pattern of results suggests that the amount of measured separability depends crucially on the way stimulus properties are defined (e.g., force versus displacement). In Experiment 2, surfaces with known perceptual properties were used to study the metric(s) of the relevant perceptual space. By specifying the perceptual, rather than the stimulus, coordinates of the surfaces, it was possible to bypass issues of perceptual separability. For surfaces of equal friction, a Euclidean metric captured the results (r²?=?0.75) more effectively than a city-block metric did; neither metric did well when differences in friction were involved. The fact that—unlike stickiness—hardness, roughness, and perceived vibration intensity are all increasing functions of surface-normal forces may facilitate their integration into a Euclidean space, in both direct (Hollins M, Bensmaïa S, Karlof K, Young F, . Individual differences in perceptual space for tactile textures: Evidence from multidimensional scaling. Percept Psychophys 62:1534–1544.) and indirect touch.     

Individual differences in perceptual switching rates; the role of occipital alpha and frontal theta band activity

Prolonged presentation of visually ambiguous figures leads to perceptual switching. Individual switching rates show great variability. The present study compares individuals with high versus low switching rates by investigating human scalp electroencephalogram and blink rates. Eight subjects viewed the Necker cube continuously and responded to perceptual switching by pressing a button. Frequent switchers showed characteristic occipital alpha and frontal theta band activity prior to a switch, whereas infrequent switchers did not. The alpha activity was specific to switching, the theta activity was generic to perceptual processing conditions. A negative correlation was observed between perceptual switching and blink rates. These results suggest that the ability to concentrate attentional effort on the task is responsible for the differences in perceptual switching rates     

Factors contributing to the integration of textural qualities: evidence from virtual surfaces

Two experiments involving indirect touch were carried out to explore the relationships among perceptual dimensions of haptically examined surfaces. Subjects in both experiments used a stylus to evaluate the properties of virtual surfaces created by a force-feedback device; four surface properties (resistance to normal force, coefficient of friction, texture scale, and vibration amplitude) were manipulated in various combinations. In Experiment 1, the extent to which there was a one-to-one relationship between specific stimulus properties and perceptual qualities ("perceptual separability") was evaluated. A substantial failure of separability was demonstrated, with friction tending to be more separable from the other properties than they were from one another. The pattern of results suggests that the amount of measured separability depends crucially on the way stimulus properties are defined (e.g., force versus displacement). In Experiment 2, surfaces with known perceptual properties were used to study the metric(s) of the relevant perceptual space. By specifying the perceptual, rather than the stimulus, coordinates of the surfaces, it was possible to bypass issues of perceptual separability. For surfaces of equal friction, a Euclidean metric captured the results (r(2) = 0.75) more effectively than a city-block metric did; neither metric did well when differences in friction were involved. The fact that-unlike stickiness-hardness, roughness, and perceived vibration intensity are all increasing functions of surface-normal forces may facilitate their integration into a Euclidean space, in both direct and indirect touch.     

Pigeons do not perceptually complete partly occluded photos of food: an ecological approach to the "pigeon problem"

Humans routinely complete partly occluded objects to recognize the whole objects. However, a number of studies using geometrical figures and even conspecific images have shown that pigeons fail to do so. In the present study, we tested whether pigeons complete partially occluded objects in a situation simulating a natural feeding context. In Experiment 1, we trained pigeons to peck at any photograph of food and not to peck at any containing a non-food object. At test, we presented both photos of food partly occluded by pigeon's feather and photos simply truncated at the same part. We predicted that if the pigeons perceptually completed the occluded portion, then they would discriminate the photos of occluded food better than the truncated photos. The result was that the pigeons pecked at the truncated photos earlier than the occluded photos. Placing the occluder next to all of the stimuli in Experiment 2 or substituting indented lozenge for the feather in Experiment 3 did not affect the results. Thus, even in a simulated ecologically significant situation, pigeons continued to not show evidence of perceptual completion.     

Effect of the number of grey levels on the detectability of a simple line signal in visual noise

The number of grey levels, G, contained in a digitized image of an external event must affect the fidelity of reproduction of that event for physical reasons. The question arises as to whether there is a separate perceptual effect of G. Three experiments are described which investigate the effect of G on the visibility of a straight-line signal in visual noise using a signal detection analysis to separate the physical and perceptual effects of G. The results show that, for the type of displays employed, and for the specific task of detection of lines in visual noise, there was no effect of G on efficiency, which suggests that G had no separate perceptual effect.