Abstract
Prolonged exposure to visual stimuli causes a bias in observers' responses to subsequent stimuli. Such adaptation-induced biases are usually explained in terms of changes in the relative activity of sensory neurons in the visual system which respond selectively to the properties of visual stimuli. However, the bias could also be due to a shift in the observer's criterion for selecting one response rather than the alternative; adaptation at the decision level of processing rather than the sensory level. We investigated whether adaptation to implied motion is best attributed to sensory-level or decision-level bias. Three experiments sought to isolate decision factors by changing the nature of the participants' task while keeping the sensory stimulus unchanged. Results showed that adaptation-induced bias in reported stimulus direction only occurred when the participants' task involved a directional judgement, and disappeared when adaptation was measured using a non-directional task (reporting where motion was present in the display, regardless of its direction). We conclude that adaptation to implied motion is due to decision-level bias, and that a propensity towards such biases may be widespread in sensory decision-making.
Highlights
Decision-making is a fundamental part of visual perception
The relatively small effect of implied motion adaptation may be due to some form of decision-level adaptation (DLA): a slight shift in the criterion for ‘left’ versus ‘right’ responses induced by inspection of directional implied motion
This paper reports a series of three psychophysical experiments designed to assess whether implied motion adaptation is best explained by sensory-level adaptation (SLA) or DLA
Summary
Decision-making is a fundamental part of visual perception. We continually make decisions about the location, speed, direction, size, etc., of visual elements in the field of view during everyday tasks. Motion adaptation experiments introduce a bias in the pattern of stimulation in favour of one direction which the visual system may attempt to neutralize by introducing a compensatory decision bias in its criterion (in favour of the opposite direction) This kind of bias would amount to recalibration or error-correction which re-labels the lines coming from stimulus-tuned neurons to ‘normalize’ skewed neural response distributions even in the absence of sensory shifts [12,13,14,15,16]. The relatively small effect of implied motion adaptation may be due to some form of DLA: a slight shift in the criterion for ‘left’ versus ‘right’ responses induced by inspection of directional implied motion Such an involvement of higher level decisional processes is consistent with a recent report [20] that visual awareness is necessary for implied motion to produce adaptation, whereas it is not necessary to produce adaptation to low-level motion [21]. We established a baseline measure of adaptation to implied motion using a standard procedure [18,20], against which we could compare later results
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