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Ru Qi Yu, Jiaying Zhao; Numerosity perception is distinct from mean or sum perception. Journal of Vision 2015;15(12):1030. doi: 10.1167/15.12.1030.
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© 2017 Association for Research in Vision and Ophthalmology.
The visual system is efficient at extracting a range of ensemble statistics. Most research has independently focused on the estimation of the number, the average, or the sum. Since these processes have been studied separately, their relationship is not well understood. Here we explore the interaction among numerosity, mean, and sum perception in one paradigm. In each trial, observers viewed an array of circles varying in size, and estimated the number, the mean size, or the total size of circles in each array in separate blocks (order counterbalanced across observers). Thus, for every array we obtained numerosity, mean, and sum estimates from the same observer. We noticed that there was consistent underestimation in the number, the mean, and the sum judgments. For every array, we also derived the arithmetic number (the estimated sum/the estimated mean), the arithmetic mean (the estimated sum/the estimated number), and the arithmetic sum (the estimated mean*the estimated number) for each observer. We found that the arithmetic mean was significantly closer to the estimated mean than to the objective mean, and the arithmetic sum was significantly closer to the estimated sum than to the objective sum. However, the estimated number was closer to the objective number than to the arithmetic number. This dissociation suggests that observers may have implicitly followed the arithmetic model for mean and sum estimation, but not for number estimation. Moreover, the errors in the sum estimates were highly correlated with the errors in the mean estimates, but the errors in the number estimates were not correlated with either the errors in the sum or the errors in the mean estimates. This provides further evidence that numerosity was calculated independently from the mean or the sum. Taken together, the results suggest that numerosity perception operates in a distinct manner from mean or sum perception.
Meeting abstract presented at VSS 2015
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