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Kymberly I. Wootton, Jennifer L. Sharp, Carl E. Granrud; Perceived size of traffic stoplights: Effects of assumed size on observers' size estimates. Journal of Vision 2004;4(8):885. doi: 10.1167/4.8.885.
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Granrud, et al. (VSS, 2003) reported that observers underestimate stoplight size at distances of 20 to 200 m, and hypothesized that observers rely on assumed size when estimating the size of a distant stoplight. Our study tested this hypothesis. Experiment 1 had two parts: a familiarization period and a test trial. During familiarization, participants (N=80) viewed a standard-sized or smaller-than-normal stoplight for 1 minute at a distance of 1 m. In the test trial, participants viewed the standard-sized or smaller-than-normal stoplight from a distance of 100 m, and estimated the size of the light's lenses by selecting, from a set of nearby comparison circles, a circle that matched the lenses' size. Test-trial size estimates conformed to the size of the stoplight seen during the familiarization period. Participants familiarized with the standard light judged its size accurately but overestimated the size of the small light. Participants familiarized with the small light judged its size accurately but underestimated the size of the standard light. The size of the stoplight seen during the test trial had no effect on size estimates. Experiment 2 (N=80) controlled for the possibility that participants responded to demand characteristics in Experiment 1. It followed the same procedures as Experiment 1, but the test-trial stoplight was viewed from a distance of 3 m. Size estimates in this experiment conformed to the size of the stoplight seen in the test trial. The stoplight seen during familiarization had no effect on estimated size. The results of these experiments support the Granrud, et al. hypothesis that observers rely on assumed size when estimating a distant stoplight's size. These findings are consistent with the hypothesis that size constancy for distant objects is not a feature of perception, and that research participants' size estimates are based on cognitive strategies in addition to visual information for size.
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