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Chad Peltier, Mark Becker; Motor Biases Do Not Account for the Low Prevalence Effect. Journal of Vision 2017;17(10):72. doi: 10.1167/17.10.72.
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© ARVO (1962-2015); The Authors (2016-present)
The low prevalence effect (LPE) is an increase in miss errors as target prevalence decreases in a visual search task. There are three proposed causes of this effect: a decrease in quitting threshold, a conservative shift in criterion, and a target absent motor bias. Per the motor bias hypothesis, the frequent target absent responses that occur in low target prevalence searches bias the target absent motor response. Occasionally this prepotent motor bias results in an erroneous target absent button press despite a target detection. Fleck and Mitroff (2007) found that the LPE was eliminated when observers could make a corrective response to overcome the prepotent target absent response. Several researchers have since found that allowing a corrective response or controlling for motor biases does not eliminate the LPE. Here we predict that motor biases will influence search performance only when the response to response time between trials is minimal. We investigate our hypothesis by allowing corrective responses under different conditions. In Experiment 1 we manipulate target prevalence and set size. Results show that motor biases contribute to the LPE only when the set size is small, thereby producing short response to response intervals between trials. In Experiment 2, we manipulate the Inter-Response-Interval (IRI) to find the time it takes to eliminate effects of motor biases on the LPE. The results show that as the IRI increases, the effects of motor biases decrease. Overall, we show that motor biases not only fail to account for the LPE, but also fail to influence search performance when target presence judgements are separated by enough time. These results indicate that researchers do not need to control for motor biases in time consuming serial search tasks and that real-world searches where trials last several seconds are unlikely to be influenced by motor biases.
Meeting abstract presented at VSS 2017
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