Academic journal article Attention, Perception and Psychophysics

A Severe Capacity Limit in the Consolidation of Orientation Information into Visual Short-Term Memory

Academic journal article Attention, Perception and Psychophysics

A Severe Capacity Limit in the Consolidation of Orientation Information into Visual Short-Term Memory

Article excerpt

Published online: 21 December 2012

(Q> Psychonomic Society, Inc. 2012

Abstract Previous research has suggested that two color patches can be consolidated into visual short-term memory (VSTM) via an unlimited parallel process. Here we examined whether the same unlimited-capacity parallel process occurs for two oriented grating patches. Participants viewed two gratings that were presented briefly and masked. In blocks of trials, the gratings were presented either simultaneously or sequentially. In Experiments 1 and 2, the presentation of the stimuli was followed by a location cue that indicated the grating on which to base one's response. In Experiment 1, participants responded whether the target grating was oriented clockwise or counterclockwise with respect to vertical. In Experiment 2, participants indicated whether the target grating was oriented along one of the cardinal directions (vertical or horizontal) or was obliquely oriented. Finally, in Experiment 3, the location cue was replaced with a third grating that appeared at fixation, and participants indicated whether either of the two test gratings matched this probe. Despite the fact that these responses required fairly coarse coding of the orientation information, across all methods of responding we found superior performance for sequential over simultaneous presentations. These findings suggest that the consolidation of oriented gratings into VSTM is severely limited in capacity and differs from the consolidation of color information.

Keywords Working memory · Visual short-term memory · Memory consolidation

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When viewing complex scenes, a great deal of visual information impinges upon the retina and is represented in early visual cortex. However, these early sensory representations are fleeting and relatively unprocessed (Sperling, 1960). In order to form visual representations that are somewhat rable and subject to masking by subsequent visual stimulation, one must consolidate the items into a more stable visual short-term memory (VSTM) representation (Becker, Pashler, & Anstis, 2000; Jolicoeur & Dell'Acqua, 1998). The contents of VSTM form the basis for oiu stable and consciously available visual representations (Chun & Potter, 1995; Phillips, 1974; Rensink, O'Regan, & Clark, 1997). As such, a great deal of research has investigated the storage capacity of this system and how the capacity and resolution of items in VSTM interact (Alvarez & Cavanagh, 2004; Awh, Barton, & Vogel, 2007; Wilken & Ma, 2004; Zhang & Luck, 2008). This research suggests that the VSTM system has a relatively fixed capacity of about three to four items, thereby establishing a fairly fundamental limit on the numbers of items that one can represent at any instant.

Despite this limit, we are able to function well in complex environments, presumably because we can rapidly select new, behaviorally relevant information from the environment and can rapidly consolidate new items into the VSTM buffer (Ballard, Hayhoe, & Pelz, 1995; O'Regan, 1992), albeit at the cost of losing some previous items within that buffer (Becker & Pashler, 2002; Wolfe, Klempen, & Dahlen, 2000). Consequently, the potential impact of the capacity limit can be minimized by efficiently altering the contents of VSTM so that the most relevant objects in the environment for one's current task are available when needed (Ballard et et al., 1995; Droll, Hayhoe, Triesch, & Sullivan, 2005; Triesch, Ballard, Hayhoe, & Sullivan, 2003). This view suggests that two processes are required for the system to function efficiently, despite VSTM capacity limits: One must be able to select relevant information from the scene for consolidation, and one must be able to rapidly consolidate that information into the VSTM system. While a great deal of research has investigated the selection of items from the environment (Desimone & Duncan, 1995; Pratt & Hommel, 2003; Soto, Hodsoll, Rotshtein, & Humphreys, 2008), little is known about the consolidation process itself. …

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