Academic journal article Perception and Psychophysics

Using Temporal Order to Identify Spatial Reference Frames

Academic journal article Perception and Psychophysics

Using Temporal Order to Identify Spatial Reference Frames

Article excerpt

A new method for identifying spatial reference frames is described and applied to the study of spatial span. In this method, a spatial sequence is displayed in relation to two reference frames that move relative to each other, so that different temporal orders are described in each reference frame. As applied to spatial span, a sequence of dots was displayed on a rectangular template that moved relative to the computer screen and the observer. Three experiments showed that the choice of reference frame is influenced by prior conditions, the size of the template, and the presence of an alternative stationary reference frame. Recall was impaired (1) when the template moved, suggesting that movement interference occurred, and (2) with increasing template size, but only if the template was used as the reference frame.

This article will describe a new method for identifying the spatial reference frame used to encode a sequence of spatial locations. The method is quite general and can be applied in any situation in which two reference frames can be moved in relation to each other in a controlled manner. Here, the method will be used to address concerns about the nature of the reference frame and the involvement of movement interference in spatial span, a task commonly used to estimate spatial short-term memory (STM). Spatial span provides an ideal vehicle for illustrating the method, so we shall first review recent findings and issues concerning spatial span and then proceed to describe the method.

Spatial Span

In spatial span, a sequence of discrete spatial locations is presented at a fixed rate in full view of an observer. The observer's task is to remember the sequence and reproduce it by pointing to the locations of the sequence in the correct order. The task was initially devised by Corsi (1972) as an analogue of digit span and was presented as an array of nine wooden blocks fixed to a rectangular board. The experimenter indicated a spatial sequence by tapping each block in succession. The Corsi task can readily be adapted to computerized presentation, in a format in which the board is shown in plan view as a rectangular frame enclosing a number of squares and the sequence is indicated by highlighting each square in turn. With computer presentation, the configuration is more flexible; for example, the positions of the squares can be varied across trials, rather than fixed, and the number of squares can vary. In addition, computer presentation allows the visibility of the tokens during presentation to be controlled. In the original Corsi task, all the possible locations, which were fixed objects, were visible throughout presentation and recall. In the form of the task used here, only one spatial token is displayed at a time during presentation, derived from the dots task developed by Jones and his colleagues (Jones, Farrand, Stuart, & Morris, 1995). In all cases, all the potential spatial locations are visible during recall, when the observer reconstructs the sequence. For a review of spatial span and its clinical applications, see Berch, Krikorian, and Huha (1998).

A number of dual-task studies have explored the effect of various kinds of interference presented concurrently with the spatial sequence or during the retention interval. These studies have consistently shown impairment caused by spatial tapping, by spatial attention shifts, and by directing eye movements to irrelevant targets (e.g., Lawrence, Myerson, & Abrams, 2004; Lawrence, Myerson, Oonk, & Abrams, 2001; Pearson & Sahraie, 2003; Smyth, 1996; Smyth & Scholey, 1994; Tremblay, Saint-Aubin, & Jalbert, 2006), but not by repetitive gestural movements that involve touching body parts (Smyth, Pearson, & Pendleton, 1988). One interpretation is mat the sequence of locations is remembered in the form of a motor plan, so that any task that engages movement control processes will produce interference. A similar account has been proposed to explain interference with visual imagery tasks (e. …

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