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Yariv Festman, Jochen Braun; Scene comprehension outside the focus of attention.. Journal of Vision 2004;4(8):128. doi: 10.1167/4.8.128.
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Expert observers discriminate elementary features (e.g., colour, orientation) of salient objects outside their current focus of attention, but not complex features such as T/L shape or colour arrangement. Surprisingly, natural scene category behaves like an elementary feature in this context, in that scenes with vehicles, animals, etc. are successfully classified in a dual-task situation (Li et al., 2002). To confirm and extend this finding, we used a similar dual-task paradigm and presented a natural scene in the near periphery (8 to 14 eccentricity) simultaneously with an attention-demanding task near fixation (seven rotated Ts/Ls). Visual persistence was controlled by a particularly effective form of masking. For scenes of animals or vehicles (black and white with matched luminance scale), categorization performance exhibited little or no attentional cost, i.e., dual- and single-task performance were comparable. Thus, scene categorization under dual-task conditions can be explained neither by inadequate masking nor by trivial colour cues. In a second experiment, observers categorized scenes from the International Affective Image System database (IAPS, Lang et al., 1995) as “pleasant” or “unpleasant”. Although absolute performance was now lower (∼75% of the level reached under ideal viewing conditions), there was no significant attentional cost. As low-level features do not identify affective content, this implies some comprehension of scene gist. A control experiment highlighted the contrast between natural scenes and geometric stimuli in the dual-task situation (and also confirmed the peripheral absence of attention), in that observers failed to discriminate the colour arrangement of a peripherally presented ‘pill’ (half red, half green, inclined ±45 ). Li FF et al. (2002) Rapid natural scene categorization in the near absence of attention. PNAS 99: 9596ff. Lang PJ et al. (1995) IAPS: Technical Manual and Affective Ratings. Gainsville, FL.
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