Set-size effects in visual search may be due to 1 or more of 3 factors: sensory processes such as lateral masking between stimuli, attentional processes limiting the perception of individual stimuli, or attentional processes affecting the decision rules for combining information from multiple stimuli. These possibilities were evaluated in tasks such as searching for a longer line among shorter lines. To evaluate sensory contributions, display set-size effects were compared with cuing conditions that held sensory phenomena constant. Similar effects for the display and cue manipulations suggested that sensory processes contributed little under the conditions of this experiment. To evaluate the contribution of decision processes, the set-size effects were modeled with signal detection theory. In these models, a decision effect alone was sufficient to predict the set-size effects without any attentional limitation due to perception.

Because of limited peripheral vision, many visual tasks depend on multiple eye fixations. Good performance in such tasks demonstrates that some memory must survive from one fixation to the next. One factor that must influence performance is the degree to which multiple eye fixations interfere with the critical memories. In the present study, the amount of interference was measured by comparing visual discriminations based on multiple fixations to visual discriminations based on a single fixation. The procedure resembled partial report, but used a discrimination measure. In the prototype study, two lines were presented, followed by a single line and a cue. The cue pointed toward one of the positions of the first two lines. Observers were required to judge if the single line in the second display was longer or shorter than the cued line of the first display. These judgments were used to estimate a length threshold. The critical manipulation was to instruct observers either to maintain fixation between the lines of the first display or to fixate each line in sequence. The results showed an advantage for multiple fixations despite the intervening eye movements. In fact, thresholds for the multiple-fixation condition were nearly as good as those in a control condition where the lines were foveally viewed without eye movements. Thus, eye movements had little or no interfering effect in this task. Additional studies generalized the procedure and the stimuli. In conclusion, information about a variety of size and shape attributes was remembered with essentially no interference across eye fixations.Many visual tasks require multiple eye fixations. To introduce the significance of multiple fixations, consider three observations: (I) vision declines with eccentricity from the center of fixation, (2) the eyes move in fixation sequences with intervening saccades, and (3) when the eyes move, widely separated objects can be perceived and remembered. These observations lead to the hypothesis that individual fixations provide samples of the visual world that are remembered and combined to support tasks such as reading, search, and recognition. More specifically, the proximal stimulus for perception is an individual fixation. Some information from the fixation is maintained in memory across eye movements. This information is combined with information from later fixations in the final percept. For lack of an established name, this commonly held hypothesis is referred to as the fixationsampling hypothesis.In this article, we consider only the memory component of this hypothesis. Furthermore, only one aspect of memory is addressed: To what extent do multiple fixations interfere with memory from a particular fixation? Previous ResearchThe effect of multiple fixations on perception and memory has been addressed by a diverse range of studies.We thankJames Cutting, David Irwin, Colin Macleod, Sandy Pollatsek, and several reviewers for useful comments on earlier versions of this article. We also thank David Irwin andMisha Pavel for man...

No abstract

In visual search, a set-size effect may be due to an attentional effect on perception or to several alternative effects. One alternative is a sensory effect such as masking and another is that attention may affect decision instead of perception. In simple search tasks such as detecting a long line among short lines, we have previously found the modest set-size effect predicted by an attentional effect on only decision. There was no evidence for any additional effect of attention on perception. To pursue this result, we investigated more complex search tasks that have been claimed to have larger attentional effects. They included tasks that required memory, tasks that used discrimination rather than detection, and tasks that used complex rather than simple shapes. Several of these tasks did yield larger set-size effects. The critical question is whether these larger set-size effects were due to an attentional effect on perception or due to one of the other possible causes.