Attentional Modulation of Binocular Rivalry

Ever since Wheatstone initiated the scientific study of binocular rivalry, it has been debated whether the phenomenon is under attentional control. In recent years, the issue of attentional modulation of binocular rivalry has seen a revival. Here we review the classical studies as well as recent advances in the study of attentional modulation of binocular rivalry. We show that (1) voluntary control over binocular rivalry is possible, yet limited, (2) both endogenous and exogenous attention influence perceptual dominance during rivalry, (3) diverting attention from rival displays does not arrest perceptual alternations, and that (4) rival targets by themselves can also attract attention. From a theoretical perspective, we suggest that attention affects binocular rivalry by modulating the effective contrast of the images in competition. This contrast enhancing effect of top-down attention is counteracted by a response attenuating effect of neural adaptation at early levels of visual processing, which weakens the response to the dominant image. Moreover, we conclude that although frontal and parietal brain areas involved in both binocular rivalry and visual attention overlap, an adapting reciprocal inhibition arrangement at early visual cortex is sufficient to trigger switches in perceptual dominance independently of a higher-level “selection” mechanisms. Both of these processes are reciprocal and therefore self-balancing, with the consequence that complete attentional control over binocular rivalry can never be realized

Time dilation in dynamic visual display

How does the brain estimate time? This old question has led to many biological and psychological models of time perception (R. A. Block, 1989; P. Fraisse, 1963; J. Gibbon, 1977; D. L. I. Zakay, 1989). Because time cannot be directly measured at a given moment, it has been proposed that the brain estimates time based on the number of changes in an event (S. W. Brown, 1995; P. Fraisse, 1963; W. D. Poynter, 1989). Consistent with this idea, dynamic visual stimuli are known to lengthen perceived time (J. F. Brown, 1931; S. Goldstone & W. T. Lhamon, 1974; W. T. Lhamon & S. Goldstone, 1974, C. O. Z. Roelofs & W. P. C. Zeeman, 1951). However, the kind of information that constitutes the basis for time perception remains unresolved. Here, we show that the temporal frequency of a stimulus serves as the “clock” for perceived duration. Other aspects of changes, such as speed or coherence, were found to be inconsequential. Time dilation saturated at a temporal frequency of 4–8 Hz. These results suggest that the clock governing perceived time has its basis at early processing stages. The possible links between models of time perception and neurophysiological functions of early visual areas are discussed

Larger Stimuli Require Longer Processing Time for Perception

The time it takes for a stimulus to reach awareness is often assessed by measuring reaction times (RTs) or by a temporal order judgement (TOJ) task in which perceived timing is compared against a reference stimulus. Dissociations of RT and TOJ have been reported earlier in which increases in stimulus intensity such as luminance intensity results in a decrease of RT, whereas perceived perceptual latency in a TOJ task is affected to a lesser degree. Here, we report that a simple manipulation of stimulus size has stronger effects on perceptual latency measured by TOJ than on motor latency measured by RT tasks. When participants were asked to respond to the appearance of a simple stimulus such as a luminance blob, the perceptual latency measured against a standard reference stimulus was up to 40 ms longer for a larger stimulus. In other words, the smaller stimulus was perceived to occur earlier than the larger one. RT on the other hand was hardly affected by size. The TOJ results were further replicated in a simultaneity judgement task, suggesting that the effects of size are not due to TOJ-specific response biases but more likely reflect an effect on perceived timing

What is Grouping during Binocular Rivalry?

During binocular rivalry, perception alternates between dissimilar images presented dichoptically. Although perception during rivalry is believed to originate from competition at a local level, different rivalry zones are not independent: rival targets that are spaced apart but have similar features tend to be dominant at the same time. We investigated grouping of spatially separated rival targets presented to the same or to different eyes and presented in the same or in different hemifields. We found eye-of-origin to be the strongest cue for grouping during binocular rivalry. Grouping was additionally affected by orientation: identical orientations were grouped longer than dissimilar orientations, even when presented to different eyes. Our results suggest that eye-based and orientation-based grouping is independent and additive in nature. Grouping effects were further modulated by the distribution of the targets across the visual field. That is, grouping within the same hemifield can be stronger or weaker than between hemifields, depending on the eye-of-origin of the grouped targets. We also quantified the contribution of the previous cues to grouping of two images during binocular rivalry. These quantifications can be successfully used to predict the dominance durations of different studies. Incorporating the relative contribution of different cues to grouping, and the dependency on hemifield, into future models of binocular rivalry will prove useful in our understanding of the functional and anatomical basis of the phenomenon of binocular rivalry

A search asymmetry for interocular conflict

When two different images are presented to the two eyes, the percept will alternate between the images (a phenomenon called binocular rivalry). In the present study, we investigate the degree to which such interocular conflict is conspicuous. By using a visual search task, we show that search for interocular conflict is near efficient (15 ms/item) and can lead to a search asymmetry, depending on the contrast in the display. We reconcile our findings with those of Wolfe and Franzel (1988), who reported inefficient search for interocular conflict (26 ms/item) and found no evidence for a search asymmetry. In addition, we provide evidence for the suggestion that differences in search for interocular conflict are contingent on the degree of abnormal fusion of the dissimilar images

The Spatial Origin of a Perceptual Transition in Binocular Rivalry

When the left and the right eye are simultaneously presented with incompatible images at overlapping retinal locations, an observer typically reports perceiving only one of the two images at a time. This phenomenon is called binocular rivalry. Perception during binocular rivalry is not stable; one of the images is perceptually dominant for a certain duration (typically in the order of a few seconds) after which perception switches towards the other image. This alternation between perceptual dominance and suppression will continue for as long the images are presented. A characteristic of binocular rivalry is that a perceptual transition from one image to the other generally occurs in a gradual manner: the image that was temporarily suppressed will regain perceptual dominance at isolated locations within the perceived image, after which its visibility spreads throughout the whole image. These gradual transitions from perceptual suppression to perceptual dominance have been labeled as traveling waves of perceptual dominance. In this study we investigate whether stimulus parameters affect the location at which a traveling wave starts. We varied the contrast, spatial frequency or motion speed in one of the rivaling images, while keeping the same parameter constant in the other image. We used a flash-suppression paradigm to force one of the rival images into perceptual suppression. Observers waited until the suppressed image became perceptually dominant again, and indicated the position at which this breakthrough from suppression occurred. Our results show that the starting point of a traveling wave during binocular rivalry is highly dependent on local stimulus parameters. More specifically, a traveling wave most likely started at the location where the contrast of the suppressed image was higher than that of the dominant one, the spatial frequency of the suppressed image was lower than that of the dominant one, and the motion speed of the suppressed image was higher than that of the dominant one. We suggest that a breakthrough from suppression to dominance occurs at the location where salience (the degree to which a stimulus element stands out relative to neighboring elements) of the suppressed image is higher than that of the dominant one. Our results further show that stimulus parameters affecting the temporal dynamics during continuous viewing of rival images described in other studies, also affect the spatial origin of traveling waves during binocular rivalry

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

Attention-based perceptual learning increases binocular rivalry suppression of irrelevant visual features

Perceptual learning refers to an improvement on a perceptual task after repeated exposure to a stimulus. It has been shown that attention can play an important role in perceptual learning. Recently, it has been suggested that training can lead to increased suppression of information that is continuously irrelevant, and that this attention-based suppression plays an important role in more efficient noise exclusion. Here we investigate this claim. Observers performed a visual speeddiscrimination task for 5 consecutive days. After training, sensitivity to motion directions that were relevant, irrelevant, or neutral toward the training task was assessed by measuring motion coherence thresholds. In addition, perceptual dominance during binocular rivalry was assessed for combinations of the three motion directions. The results showed that sensitivity to the task-relevant feature increased due to training. That is, motion coherence thresholds were selectively lowered for the task-relevant feature. Interestingly, the feature that was task-irrelevant during training was more strongly suppressed during binocular rivalry: The mean perceptual dominance of this feature was selectively decreased. Our results show that task-irrelevant information that potentially interferes with the primary task during learning gets more strongly suppressed. Furthermore, our results add new evidence in support of the claim that mechanisms involved in visual attention and binocular rivalry overlap. Introduction Perceptual learning refers to an improvement in performance on a perceptual task after repeated practice or exposure to a certain stimulus It has been shown that learning is more effective when the task-relevant visual signal is embedded in noise The role of attention in perceptual learning has also been studied using electrophysiological recordings in behaving animals In the present study, we investigate how learninginduced changes in the processing of visual features that were task relevant and task irrelevant during training will affect perceptual dominance of these features in binocular rivalry. In particular, we hypothesized that probing learning effects using binocular rivalry can provide evidence of increased suppression of task-irrelevant information due to training. During binocular rivalry, dissimilar images presented dichoptically compete for perceptual dominance Method Observers Six naïve observers participated in the experiments. All observers had normal or corrected-to-normal vision. Apparatus and stimuli The stimuli used in the different experiments are schematically illustrated in General procedure Each observer performed in 3 experiments on 7 days. The maximum time allowed between sessions was 2 days. On day 1 and day 7, coherence thresholds were assessed for rightward (task-relevant), downward (task-irrelevant), and left-upward (task-neutral) motion. Also on day 1 and 7, perceptual dominance of combinations of these motion directions was assessed in the binocular rivalry experiment. On day 2 through 6, observers performed a speeddiscrimination task for 30 min. For each experiment, observers viewed the stimuli at a distance of 57 cm from the monitor, with viewing distance restrained by a chinrest. Motion coherence experiment Motion coherence thresholds were acquired in separate blocks for each motion direction using a 3-1 adaptive staircase procedure arriving at a 79% correct threshold. A single trial consisted of 2 intervals, each 0.5 s in duration and separated by 1 s, one of which contained coherent motion in one of the 3 directions (rightward, downward, or left-upward), and one of which contained no coherent motion. The order of the two intervals was randomized from trial to trial. A single staircase terminated after 10 reversals. For each motion direction, 2 staircases (one starting at 0 and one starting 60% coherence) were randomly interleaved within one session. Thresholds were calculated by taking the mean of 9 staircases (where the mean of a single trail was based on the last 3 reversals in the staircase). Binocular rivalry experiment Perceptual dominance of the different motion directions was assessed by dichoptically presenting rightward versus downward, rightward versus left-upward, and downward versus left-upward motion. All random dot stimuli contained 100% coherent motion. The speed of individual dots was constant at 3.2 deg/s. A single trial lasted 30 s. . Schematic illustration of stimuli and conditions. A. The coherence threshold experiment. Before and after training, observers had to indicate which of two intervals contained global motion. By varying the percentage of dots moving in a single direction, 79% correct thresholds for rightward, downward, and left-upward were acquired. Thresholds were acquired using a staircase procedure (see text). B. The binocular rivalry experiment. Before and after training, observers continuously indicated which of two rivaling motion directions was perceptually dominant. Rival stimuli were rightward versus downward (relevant versus irrelevant; upper panel), rightward versus left-upward (relevant versus neutral; middle panel), and downward versus left-upward (irrelevant versus neutral; lower panel). C. The training experiment. On 5 consecutive days, observers indicated which of two intervals contained faster rightward motion. The speed of the vertical motion dots was constant; the speed of rightward motion was constant in one interval, and varied in the other. Journal of Vision Training On each training day, observers performed a 2-interval forced-choice speed-discrimination task. Each interval contained both downward and rightward motion. The speed of the downward motion was constant (at 3.2 deg/s) throughout the training sessions. The speed of the rightward motion was fixed for one of the two intervals (at 3.2 deg/s), while that of the other interval was varied between 1.6 and 4.8 deg/s (using the method of constant stimuli). The motion coherence of both motion directions was 100%. Observers were instructed to indicate which of the two intervals contained faster rightward motion. The experiment involved 25 trials per condition per training day. Results Performance in the speed-discrimination task during the 5-day practice sessions is displayed in Training had a significant effect on the sensitivity to the motion direction that was relevant during training. In Figures 3B and 3C display data for the binocular rivalry experiments performed before and after training. The figures represent the change in dominance after training compared to before training. From Discussion The main finding of the present study is that visual features that were task irrelevant throughout the training sessions were more strongly suppressed during binocular rivalry in the post-training compared to pre-training tests. These results show that learning results in stronger inhibition of irrelevant visual information that is present during training. In this respect, our findings are in agreement with a study by Journal of Vision A puzzling aspect of our results is that learning-induced changes in direction sensitivity and binocular rivalry took place while improvement on the speed-discrimination task was absent. A possible reason for this might be that it has been reported that processing of speed and direction of visual motion can be independent The increase in sensitivity for the task-relevant feature is in accordance with recent findings using a similar learning procedure Another implication of the present study is that the effect of training is highly specific to the task used: in the binocular rivalry experiment, task-irrelevant information became less dominant (reflecting increased suppression of this feature), while dominance of task-relevant information was unaffected; in the coherence experiment on the other hand, sensitivity to task-relevant information was increased, while sensitivity to task-irrelevant information was unaffected. What can explain the different effects of training on motion coherence thresholds on the one hand, and on perceptual dominance during binocular rivalry on the other? To gain insight into this issue, it is informative to look at the visual processing stages that are thought to be involved in motion coherence tasks and in binocular rivalry. Global motion is generally believed to be computed at the level of the human homologue of monkey middle temporal (MT) and medial superior temporal (MST) area Journal of Vision A question that remains is why the increased sensitivity to the task-relevant feature was not reflected by increased dominance for this feature. The answer to this question can possibly lie in the fact that sensitivity to a certain visual feature does not necessarily correspond to the magnitude of perceptual dominance during binocular rivalry. For example, Fahle (1982) showed that a spatial frequency to which observers are usually most sensitive (which is around 3 cpd) does not make the most dominant stimulus during binocular rivalry. Also, oblique orientations (to which sensitivity is lower compared to horizontal and vertical orientations) do not have a lower perceptual dominance compared to horizontal or vertical orientations The results of the binocular rivalry experiments indicate that the stimulus feature that was irrelevant to the demands of the training task was more strongly suppressed when engaged in binocular rivalry. It is of interest to see our results in the framework of Levelt's second proposition The discrepancy between what would be expected from Conclusions The present study shows that attentional suppression of task-irrelevant information increases with training. In addition, our results show that this training-induced suppression of task-irrelevant information can be accompanied by increased sensitivity for task-relevant information. We suggest that this attention-based suppression occurs when task-irrelevant information is strong enough to interfere with processing of the behaviorally relevant information in the stimulus. Next to the implications on perceptual learning, our study provides new evidence regarding the proposed link between visual attention and binocular rivalr