Academic journal article Perception and Psychophysics

Looking at Scenes While Searching for Numbers: Dividing Attention Multiplies Space

Academic journal article Perception and Psychophysics

Looking at Scenes While Searching for Numbers: Dividing Attention Multiplies Space

Article excerpt

Observers tend to remember seeing a greater expanse of a scene than was shown (boundary extension [BE]). Is undivided visual attention necessary for BE? In Experiment 1, 108 observers viewed photographs with superimposed numerals (2s and 5s). Each appeared for 750 msec, followed by a masked interval and a test picture (same, closer up, or wider angled). Test pictures were rated as the same, closer, or wider angled on a 5-point scale. Visual attention was manipulated with a search task: The observers reported the number of 5s (zero, one, or two). The observers performed search only, picture rating only, or both (giving search priority). Search accuracy was unaffected by condition. BE occurred in both conditions but was greater with divided attention. The results were replicated using incidental BE tests (Experiments 2 and 3). We propose that anticipatory representation of layout occurs automatically during scene perception, with focal attention serving to constrain the boundary error.

The visual world is continuous, but physiological constraints prevent us from seeing it all at once. Instead, we sample the environment through movements of the head, body, and eyes. How are successive views integrated within a coherent representation of surrounding space? A common error in scene representation, called boundary extension (BE), may provide part of the answer (Intraub & Richardson, 1989; for a review, see Intraub, 2007). When viewers explicitly attempt to remember the objects, details, and layout of a scene, they tend to remember more than was actually shown. Their mental representations appear to anticipate the continuity of layout inherent in real-world scenes, which may serve to support integration of successive views into a coherent spatial framework (Gottesman & Intraub, 2002; Intraub, 1997).

BE occurs rapidly and has been observed following a masked interruption to sensory input as brief as 42 msec (an interval commensurate with the duration of a saccade; Dickinson & Intraub, 2008). Behavioral experiments (e.g., Gottesman & Intraub, 2002; Intraub, Gottesman, & Bills, 1998) and neuroimaging research (Park, Intraub, Yi, Widders, & Chun, 2007) indicate that it is specifically associated with the processing of layout-an aspect of scene structure that continues beyond the edges of a view. BE appears to occur across the life span. Memory tests revealed layout extrapolation in scene memory for individuals ranging in age from 6 to 84 years old (Seamon, Schlegel, Hiester, Landau, & Blumenthal, 2002). Infants as young as × months of age exhibited looking preferences, suggesting that they too remember having seen more of a view than was shown (Quinn & Intraub, 2007). It is tempting to conclude that BE is a fundamental aspect of scene representation.

However, the extant literature on BE includes only cases in which observers were presented with a single task. In all BE experiments (with the exception of the infant study, of course), observers were explicitly instructed to memorize each scene for a later memory test. However, in the case of our normal day-to-day scene perception, we do not attempt to memorize each scene that comes into view. In fact, the scene through which we navigate is often incidental to the specific task at hand (e.g., we search for street signs and house numbers as we drive through an unfamiliar neighborhood, while houses and terrain roll by). If BE plays a fundamental role in scene perception, it should occur in such situations as well. On the other hand, if it is related solely to the task of memorizing a view, its utility for everyday scene perception would, at best, be limited, and it surely could not play an important role in view integration. The purpose of our research was to determine whether BE would occur when scene memory was neither the sole task nor the primary task of the observer-that is, when a scene is in the background while visual attention is focused on a demanding, unrelated task in the foreground. …

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