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Where What You Count is What Really Counts

Where What You Count is What Really Counts Nader Noori (nnoori@usc.edu), Laurent Itti (itti@usc.edu) Department of Computer Science, University of Southern California Los Angeles, CA 90089 USA Abstract We noticed that human subjects were notably faster and more accurate in concurrent counting of three location-based events while they ignored the identity of targets, compared to concur- rent counting of three identity-based events while they ignored the locations. In a control experiment, subjects performed a location-based triple counting task, while now also paying at- tention to the target identity. This did not incur any additional cost, compared to the cost of the location-based counting. Per- forming each of these tasks relies on maintaining three run- ning numerical counters, and on switching between them to increase each one. Our results suggest that switching between these counters has lower cost when they are associated to spa- tial locations, compared to when they are associated to identi- ties. This difference is not affected when additionally process- ing the identity of items. We argue that this might be related to the advantage of the space in switching attention between internal representations. Keywords: Symbolic Working Memory; Working Memory; Spatial Strategies; Spatial Registry; Visuospatial Short-Term Memory; Concurrent Counting; Triple Counting; Focus of At- tention. Introduction The challenge of many non-trivial intellectual symbolic working memory tasks lies in the difficulty of juggling sev- eral residents of working memory at the same time; there are one or two items that are being acted upon while a few oth- ers are actively maintained and kept apart for future steps of the process. For example think of adding 34 to 89 mentally while looking away from the paper or the screen. During early mathematics education, students are taught to perform this task in a sequential way, and by several calls on the addi- tion table for single-digit numbers. In this example, while 3 and 8 (or 30 and 80?) are maintained for the next step of the operation, 9 and 4 are the ones that are acted upon first. Due to the increasing role of abstract representations in solving difficult problems, intellectual symbolic tasks such as this example have become increasingly important as a part of necessary mental skills for a civilized individual in mod- ern time. Understanding our limitations in maintaining and manipulating mental concepts that are needed for intellectual tasks is key to understanding our cognitive limitations, and to possibly improving individuals’ performance. This in turn poses the question of how we manage to keep some items in our working memory, and how we can handle selecting them for the right operation at the right time. The common metaphor among cognitive psychologists, which captures the selectivity of operations on several ac- tively maintained items, is the shiftable spotlight or focus of attention. Attention in this sense refers to the special treat- ment that a few representations receive, which in turn makes it possible to be acted upon (or processed) with more agility (in terms of response time or accuracy). Cowan goes even further and uses the concept of attention to directly relate working memory representations to long- term memory representations. In his view, residents of work- ing memory are those representations in long-term memory which have received attention. He states that this attention may apply to only four items at a time, and hence the num- ber of representations in working memory is limited to four (Cowan, 1999). Some other researchers have mentioned that indeed the spotlight of attention is even narrower than four items, and there is room for only one representation (Garavan, 1998; McElree, 2001). Experimental support for this claim comes from the observation that the most recently attended resident of working memory is privileged in terms of process- ing speed (McElree & Dosher, 1989; Mcelree, 2006; Gara- van, 1998; Voigt & Hagendorf, 2002). For example Garavan studied the execution time of human subjects in a self-paced dual counting task where subjects had to keep count of how many of two possible visual shapes (triangles versus squares) had been presented. The sequence of switching between in- ternally maintained counters is dictated by the stimulus se- quence of triangles and squares. Garavan noticed that updat- ing a recently updated counter (e.g., when two squares or two triangles are presented consecutively) is significantly faster than updating alternative counters (e.g., when a square is pre- sented after a triangle or vice-versa). Garavan showed that this speedy update of a recently updated internal counter is not related to the perceptual priming in detecting the asso- ciate signal. He posited that the execution time difference be- tween updating one counter twice and updating two different counters is related to the cost of shifting the focus of attention from one counter to the other one. Oberauer has tried to reconcile Cowan’s concept of atten- tion with the single spotlight focus of attention, to estab- lish a framework that explains storage and processing as two features of working memory (Oberauer, 2002). While the concept of shifting the focus of attention seems to capture the dynamics of working memory during mental processing, one question remains to be answered: what is the underly- ing mechanism for switching between two working memory representations? In particular, is there a unitary system for switching attention between items of working memory, either in space or in other dimensions? For this matter, some researchers have looked at brain ac- tivities of human subjects during tasks that involve reconfig- uration of cognitive resources by switching between differ- ent representations. Yantis and his colleagues, in a series of fMRI studies, have compared BOLD signals during switch- ing attention in the visual-spatial domain or in other repre- sentation domains. They have identified a fronto-parietal net-