Task-driven and flexible mean judgment for heterogeneous luminance ensembles
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40 YEARS OF FEATURE INTEGRATION: SPECIAL ISSUE IN MEMORY OF ANNE TREISMAN
Task-driven and flexible mean judgment for heterogeneous luminance ensembles Yusuke Takano 1 & Eiji Kimura 2
# The Psychonomic Society, Inc. 2019
Abstract Spatial averaging of luminances over a variegated region has been assumed in visual processes such as light adaptation, texture segmentation, and lightness scaling. Despite the importance of these processes, how mean brightness can be computed remains largely unknown. We investigated how accurately and precisely mean brightness can be compared for two briefly presented heterogeneous luminance arrays composed of different numbers of disks. The results demonstrated that mean brightness judgments can be made in a task-dependent and flexible fashion. Mean brightness judgments measured via the point of subjective equality (PSE) exhibited a consistent bias, suggesting that observers relied strongly on a subset of the disks (e.g., the highest- or lowest-luminance disks) in making their judgments. Moreover, the direction of the bias flexibly changed with the task requirements, even when the stimuli were completely the same. When asked to choose the brighter array, observers relied more on the highest-luminance disks. However, when asked to choose the darker array, observers relied more on the lowest-luminance disks. In contrast, when the task was the same, observers’ judgments were almost immune to substantial changes in apparent contrast caused by changing the background luminance. Despite the bias in PSE, the mean brightness judgments were precise. The justnoticeable differences measured for multiple disks were similar to or even smaller than those for single disks, which suggested a benefit of averaging. These findings implicated flexible weighted averaging; that is, mean brightness can be judged efficiently by flexibly relying more on a few items that are relevant to the task. Keywords Ensemble perception . Summary statistics . Averaging . Brightness . Lightness
The visual system can summarize complex scenes by rapidly forming statistical summary descriptions of sets of similar items. For example, rapid and accurate averaging has been reported with many visual features, including motion (Watamaniuk & Duchon, 1992; Watamaniuk, Sekuler, & Williams, 1989), orientation (Dakin & Watt, 1997; Parkes, Lund, Angelucci, Solomon, & Morgan, 2001), and size (Ariely, 2001; Chong & Treisman, 2003, 2005; for reviews, see Alvarez, 2011; Bauer, 2015; Whitney, Haberman, & Electronic supplementary material The online version of this article (https://doi.org/10.3758/s13414-019-01862-w) contains supplementary material, which is available to authorized users. * Eiji Kimura [email protected] 1
Graduate School of Science and Engineering, Chiba University, Chiba-shi, Chiba, Japan
2
Department of Psychology, Graduate School of Humanities, Chiba University, Chiba-shi, Chiba, Japan
Sweeny, 2014). Such statistical processing, called ensemble coding, has also been found for higher-level properties of images, inc
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