Abstract
The contribution of sensory and decisional processes to perceptual decision making is still unclear, even in simple perceptual tasks. When decision makers need to select an action from a set of balanced alternatives, any tendency to choose one alternative more often-choice bias-is consistent with a bias in the sensory evidence, but also with a preference to select that alternative independently of the sensory evidence. To decouple sensory from decisional biases, here we asked humans to perform a simple perceptual discrimination task with two symmetric alternatives under two different task instructions. The instructions varied the response mapping between perception and the category of the alternatives. We found that from 32 participants, 30 exhibited sensory biases and 15 decisional biases. The decisional biases were consistent with a criterion change in a simple signal detection theory model. Perceptual decision making, thus, even in simple scenarios, is affected by sensory and decisional choice biases.
Highlights
You ask a friend about the tilt of a canvas that is perfectly horizontal and she says that the top right corner is up
We will refer to these as global choice biases. The existence of these biases is acknowledged (Gold and Ding, 2013; Kingdom and Prins, 2016; Morgan et al, 2012; Garcıa-Perez and Alcala-Quintana, 2013; Peters et al, 2016) and they are included in current models of perceptual decision making (Abrahamyan et al, 2016; Akaishi et al, 2014; Urai et al, 2017; Braun et al, 2018; HermosoMendizabal et al, 2019), but whether they reflect sensory or decisional processes has not been, to our knowledge, assessed
In a simple discrimination task with two symmetric alternatives, most people exhibit idiosyncratic global choice biases
Summary
You ask a friend about the tilt of a canvas that is perfectly horizontal and she says that the top right corner is up. One possibility is that her sensory representation is biased and she perceives the canvas tilted Another possibility, is that under uncertainty about the orientation of the canvas, she prefers to choose up over down. This situation exemplifies a major problem in the study of perception: perceptual decisions depend on the sensory evidence, and on decisional components (Green and Swets, 1966; Gold and Ding, 2013). Choice biases occur in perceptual tasks even in simple scenarios like the one described above, in which the stimuli carry similar levels of signal relative to a neutral point (Newsome and Pare, 1988; Mareschal and Clifford, 2012; Jazayeri and Movshon, 2007; Milner et al, 1992; Tadin et al, 2003)
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