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Mind the gap: the cost of looking at nothing, or the performance implications of memory-induced attention shifts

Mind the Gap: The Cost of Looking at Nothing, or the Performance Implications of Memory-induced Attention Shifts Ivan Vankov (i.i.vankov@gmail.com) Central and East European Center for Cognitive Science New Bulgarian University, 21 Montevideo Street, Sofia 1618, Bulgaria Abstract The visual indexing theory proposed by Zenon Pylyshyn predicts that visual attention mechanisms are employed when projecting mental images onto a visual scene. Recent eye- tracking have supported this hypothesis by showing that people tend to look at empty places, where requested information has been previously presented. However it remained unclear what performance implications this behavior has. The present study aimed to explore how the relative location of presentation affects performance in tasks involving recalling whether an object has already been seen. Experiment 1 demonstrated that recalling objects which have been presented away from the current focus point results in slower reaction times. Experiment 2 showed that a spatial compatibility effect arises if the relative location of the memorized object is incompatible with a spatial task at hand. Keywords: attention; memory; space; visual imagery; spatial compatibility; Simon effect Introduction The visual indexing theory proposed by Zenon Pylyshyn (Pylyshyn, 1989) stipulates that there is a pre-attentive mechanism in the visual system for individuating features and indexing their locations within the visual field. Once such location indexes are formed, they serve to bind together the features of an object and maintain its identity. The indexes are also used to refer to information which was bound to a certain location in the visual field and guide visual attention. One of the major implications of visual indexing theory is that visual indexes are used to direct attention not only when attending directly perceivable stimuli, but also when projecting mental images onto some visual scene (Pylyshyn, 1998). Recent eye-tracking studies have rendered support for this hypothesis by showing that people look at empty spaces where requested information has previously been presented (Richardson & Spivey, 2000; Spivey & Geng, 2001; Hoover & Richardson, 2008). For example, Spivey and Geng (2001) asked participants to memorize a set of four simple shapes displayed at the corner cells of a 3x3 grid. The display then vanished and reappeared with one of the objects missing. When asked about the properties of the missing object, participants spontaneously looked at the blank region where the object had been previously presented. These results were interpreted in terms of the visual indexing theory: the missing object identity had been bound to a specific location in the visual field and attempting to access any information about the object resulted in an attention shift towards that location. An important question that remained unexplored by the eye-tracking studies was whether the attention shifts towards locations of previously seen objects were related to memory performance. If attention shifts are employed in the retrieval process, then one would expect that their processing costs would be reflected in the speed with which objects are recalled. In other words, the question is whether one would need more time to retrieve information which was presented away from the current focus point compared to when it was at the same location. The results of previous studies focused on the interplay of memory and visual imagery suggest that indeed the relative location of a target item within a visual image affects memory performance. The seminal work of Kosslyn, Ball and Reiser (1978) demonstrated that people needed more time to mentally scan further distances across visual images, even when the same amount of material fell between the initial focus point and the target. However, Kosslyn and colleagues explicitly asked the participants to base their responses on their visual mental images and when this instruction was omitted, the effect of distance disappeared. Thus, the first goal of the present study was to investigate whether it is possible to show an effect of the relative location of a memorized item on performance in a purely memory task even if no explicit instructions for employing visual imagery are given. A second issue which remains is what consequences the memory-driven redirection of attention would have if subjects are given a task requiring them to respond on the basis of available spatial information. To this end, a task was selected which has both memory retrieval and spatial judgment components. If the memory retrieval aspect of the task induces attention shifts, then they may happen to be incompatible with some of the responses and thus a spatial compatibility effect would be observed. A spatial compatibility effect, usually referred to as a Simon effect (Simon & Rudell, 1967), denotes faster and more accurate responses when the task-irrelevant stimulus’ location is compatible with a response action than when it is not. Several researches have advocated that the Simon effect is related to attention shifts (Nicoletti & Umilta, 1994; Rubichi at el, 1997). According to the attention shift account, directing attention to a location in space facilitates actions towards that position. Hence, there are good reasons to expect that attention shifts generated in the process of memory retrieval may cause Simon-like effects.