Are integrated objects the unit of capacity of visual working memory, or is continued attention needed to maintain bindings between independently stored features? In a delayed recall task, participants reported the color and shape of a probed item from a memory array. During the delay, attention was manipulated with an exogenous cue. Recall was elevated at validly cued positions, indicating that the cue affected item memory. On invalid trials, participants most frequently recalled either both features (perfect object memory) or neither of the two features (no object memory); the frequency with which only one feature was recalled was significantly lower than predicted by feature independence as determined in a single-feature recall task. These data do not support the view that features are remembered independently when attention is withdrawn. Instead, integrated objects are stored in visual working memory without need for continued attention.
The extraction of the distance between an object and an observer is fast when angular declination is informative, as it is with targets placed on the ground. To what extent does angular declination drive performance when viewing time is limited? Participants judged target distances in a real-world environment with viewing durations ranging from 36–220 ms. An important role for angular declination was supported by experiments showing that the cue provides information about egocentric distance even on the very first glimpse, and that it supports a sensitive response to distance in the absence of other useful cues. Performance was better at 220 ms viewing durations than for briefer glimpses, suggesting that the perception of distance is dynamic even within the time frame of a typical eye fixation. Critically, performance in limited viewing trials was better when preceded by a 15 second preview of the room without a designated target. The results indicate that the perception of distance is powerfully shaped by memory from prior visual experience with the scene. A theoretical framework for the dynamic perception of distance is presented.
Visual perception of absolute distance (between an observer and an object) is based upon multiple sources of information that must be extracted during scene viewing. The viewing duration needed to fully extract distance information, particularly in navigable real-world environments, is unknown. In a visually-directed walking task, a sensitive response to distance was observed with 9-ms glimpses when floor- and eye-level targets were employed. However, response compression occurred with eye-level targets when angular size was rendered uninformative. Performance at brief durations was characterized by underestimation, unless preceded by a block of extended-viewing trials. The results indicate a role for experience in the extraction of information during brief glimpses. Even without prior experience, the extraction of useful information is virtually immediate when the cues of angular size or angular declination are informative.
The ground plane is thought to be an important reference for localizing objects, particularly when angular declination is informative, as it is for objects seen resting at floor level. A potential role for eye movements has been implicated by the idea that information about the nearby ground is required to localize objects more distant, and by the fact that the time course for the extraction of distance extends beyond the duration of a typical eye fixation. To test this potential role, eye movements were monitored when participants previewed targets. Distance estimates were provided by walking without vision to the remembered target location (blind walking) or by verbal report. We found that a strategy of holding the gaze steady on the object was as frequent as one where the region between the observer and object was fixated. There was no performance advantage associated with making eye movements in an observational study (Experiment 1) or when an eye-movement strategy was manipulated experimentally (Experiment 2). Observers were extracting useful information covertly, however. In Experiments 3 through 5, obscuring the nearby ground plane had a modest impact on performance; obscuring the walls and ceiling was more detrimental. The results suggest that these alternate surfaces provide useful information when judging the distance to objects within indoor environments. Critically, they constrain the role for the nearby ground plane in theories of egocentric distance perception.
How sensitive are viewers to changes in global image properties across saccades during active real-world scene perception? This question was investigated by globally increasing and/or decreasing luminance or contrast in photographs of real-world scenes across saccadic eye movements or during matched brief interruptions in a flicker paradigm. The results from two experiments demonstrated very poor sensitivity to global image changes in both the saccade-contingent and flicker paradigms, suggesting that the specific values of basic sensory properties do not contribute to the perception of stability across saccades during complex scene perception. In addition, overall sensitivity was significantly worse in the saccade-contingent change paradigm than the flicker paradigm, suggesting that the flicker paradigm is an imperfect simulation of transsaccadic vision.
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