An uninformative exogenous cue speeds target detection if cue and target appear in the same location separated by a brief temporal interval. This finding is usually ascribed to the orienting of spatial attention to the cued location. Here we examine the role of perceptual merging of the two trial events in speeded target detection. That is, the cue and target may be perceived as a single event when they appear in the same location. If so, cueing effects could reflect, in part, the binding of the perceived target onset to the earlier cue onset. We observed the traditional facilitation of cued over uncued targets and asked the same observers to judge target onset time by noting the time on a clock when the target appeared. Observers consistently judged the onset time of the target as being earlier than it appeared with cued targets judged as earlier than uncued targets. When the event order is reversed so that the target precedes the cue, perceived onset is accurate in both cued and uncued locations. This pattern of results suggests that perceptual merging does occur in exogenous cueing. A modified attention account is discussed that proposes reentrant processing, evident through perceptual merging, as the underlying mechanism of reflexive orienting of attention.
When storing multiple objects in visual working memory, observers sometimes misattribute perceived features to incorrect locations or objects. These "swaps" are usually explained by a failure to store object representations in a bound form. Swap errors have been demonstrated mostly in simple objects whose features (color, orientation, shape) are easy to encode independently. Here, we tested whether similar swaps can occur with real-world objects where the connections between features are meaningful. In Experiment 1, observers were simultaneously shown four items from two object categories (two exemplars per category). Within a category, the exemplars could be presented in either the same (two open boxes) or different states (one open, one closed box). After a delay, two exemplars drawn from one category were shown in both possible states. Participants had to recognize which exemplar went with which state. In a control task, they had to recognize two old vs. two new exemplars. Participants showed good memory for exemplars when no binding was required. However, when the tested objects were shown in the different states, participants were less accurate. Good memory for state information and for exemplar information on their own, with a significant memory decrement for exemplar-state combinations suggest that binding was difficult for observers and "swap" errors occurred even for real-world objects. In Experiment 2 we used the same tasks, but on half of trials the locations of the exemplars were swapped at test. We found that participants ascribed incorrect states to exemplars more frequently when the locations were swapped. We conclude that the internal features of real-world objects are not perfectly bound in VWM and can be attached to locations independently. Overall, we provide evidence that even real-world objects are not stored in an entirely bound representation in working memory.
Numerous studies report that observers are good at evaluating various ensemble statistics, such as mean or range. Recent studies have shown that, in the perception of mean size, the visual system relies on size information individually rescaled to distance for each item (Utochkin & Tiurina, 2018). Here, we directly tested this rescaling mechanism on the perception of variance. In our experiment, participants were stereoscopically shown a sample set of circles with different sizes and in different apparent depths. Then they had to adjust a test set so that the range of sizes to match the range of the sample. We manipulated the correlation between sizes and depth for both samples and tests. In positive size-depth correlation, bigger circles were presented farther and had to seem larger and small circles were presented closer and had to seem smaller; therefore, the apparent range had to increase. In negative size-depth correlation, the apparent range had to decrease, since bigger circles had to become smaller, and vice versa. We tested all possible couplings of correlation conditions between samples and tests. We found that in general, observers tended to overestimate the range of the sample (over-adjusted it on the test). Yet, the strongest underestimation was shown when the sample had a negative correlation and the test had a positive correlation. This pattern is consistent with the prediction following from the idea of rescaling. As the negative correlation reduced an apparent range, participants had to under-adjust the range of a positively correlated test to compensate for the difference in variance impressions. We conclude, therefore, that multiple sizes are automatically rescaled in accordance with their distances and this rescaling can be used to judge ensemble variance.
Illusory conjunctions (IC) refer to errors in which an observer correctly reports features present in the display, but incorrectly pairs features or parts from multiple objects. There is a long-standing debate in the literature about the nature of ICs; for example, whether they arise from the lack of focused attention (Treisman & Schmidt, 1982) or from lossy peripheral representations (Rosenholtz et al., 2012). Here, we test the hypothesis that the occurrence of ICs relates to spatial uncertainty of features falling within the same noisy “window”. According to this idea, ICs occur when the spatial uncertainty is large compared to the distance between items, causing confusion over which features belong to which item. In Experiment 1, we directly measured the spatial noise at 3°, 6°, 9°, 12° from fixation. A compact “crowd” of four dots briefly appeared, followed by the presentation of a probe circle at various distances from the “crowd”. Observers had to respond whether any dot had fallen within the probed region. The probability of perceiving the dots as outside the probe as a function of distance provides a measure of spatial noise as a function of eccentricity. In Experiment 2, we presented four differently colored and oriented bars, located on an invisible circle with a diameter varying from 1° to 3.5° (the “separation”), and centered at one of three eccentricities (4°, 8°, 12°). Participants had to report the color, orientation, and location of any of the bars. The number of correct answers, guesses (reporting non-presented features), and ICs were estimated. The number of IC increased with eccentricity and decreased with separation. There is good resemblance between the spatial noise and the IC pattern. We conclude that there can be an overlap between the mechanisms of spatial localization and IC in peripheral vision.