Search

One of the classic problems in perception concerns how we perceive a stable, continuous visual world even though we view it via a temporally discontinuous series of eye movements. Previous investigators have suggested that our perception of a stable visual environment is due to anintegrative visual buffer, a special memory store capable of fusing the visual contents of successive fixations according to their environmental coordinates. In this paper, three experiments are reported that attempted to demonstrate the existence of an integrative visual buffer. The experimental procedure required subjects to mentally fuse two halves of a dot matrix presented in the same spatial region of a display, but separated by an eye movement so that each half was viewed only during one fixation. Thus, subjects had to integrate packets of visual information that had the same environmental coordinates, but different retinal coordinates. No evidence was found in any experiment for the fusion of visual information from successive fixations in memory, leaving the status of the integrative visual buffer in serious doubt.

A partial processing hypothesis is proposed to account for performance under a visual search condition where target and field items belong to the different conceptual categories, letter and digit (between-category search), as compared to a condition in which they belong to the same category (within-category search). This hypothesized mechanism implies that less information is registered and/or retained in between- than in within-category search. This prediction was tested and confirmed in three experiments. The results indicate that both targets and field items are processed less deeply in between- than in within-category search.

Prior studies have shown that between-category visual search (e.g., looking for a “6” among letters) is easier that within-category search (e.g., looking for a “6” among other digits). Four experiments were performed to determine what particular benefits are conferred in between-category search. The first experiment demonstrates that this category-effect occurs even when the subject has to identify the target, this suggests that the between-category search can “tag” the categorially different item for further processing. Three further experiments provide evidence that this tag is based on the item’s spatial location within the array.

Sixty Ss were each presented 120 random sequences of 9 of the 10 digits (0–9); their task on each trial was to supply the missing digit. Two stimulus input rates and two response time limits were combined factorially to yield four experimental conditions. Contrary to expectation, evidence seeming to support the use of a strategy based on the ordinal properties of the stimuli was found only when rapid (1-sec) responses were required, regardless of input rate. It is suggested that this result is most reasonably attributed to the operation of a guessing bias for numbers in the middle of the ordinal sequence. Differences in the constitution of the stimulus series may account for the failure to confirm previous findings of an ordinal strategy.

Evidence is presented for a processing mechanism in visual recognition that depends upon how the stimulus array is conceptually categorized rather than upon its physical characteristics. Ss had to detect a letter or digit target in a field of letters or digits. When target and field were of the same category, reaction time increased with display size. When target and field category differed, reaction times were independent of display size. This category effect held even for the ambiguous target character 0 that yielded reaction time functions appropriate to how it was specified prior to presentation: as “zero” or as “ō.”