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A mathematical model for distinguishing bias from sensitivity effects in multialternative detection tasks

Studies investigating the neural bases of cognitive phenomena such as perception, attention and decision-making increasingly employ multialternative task designs. It is essential in such designs to distinguish the neural correlates of behavioral choices arising from changes in perceptual factors, such as enhanced sensitivity to sensory information, from those arising from changes in decisional factors, such as a stronger bias for a particular response or choice (choice bias). To date such a distinction is not possible with established approaches. Thus, there is a critical need for a theoretical approach that distinguishes the effects of changes in sensitivity from those of changes in choice bias in multialternative tasks. Here, we introduce a mathematical model that decouples choice bias from perceptual sensitivity effects in multialternative detection tasks: multialternative tasks that incorporate catch trials to measure the ability to detect one among multiple (potential) stimuli or stimulus features. By formulating the perceptual decision in a novel, multidimensional signal detection framework, our model identifies the distinct effects of bias and sensitivity on behavioral choices. With a combination of analytical and numerical approaches, we demonstrate that model parameters (sensitivity, bias) are estimated reliably and uniquely, even in tasks involving arbitrarily large numbers of alternatives. Model simulations revealed that ignoring choice bias or performance during catch trials produced systematically inaccurate estimates of perceptual sensitivity, a finding that has important implications for interpreting behavioral data in multialternative detection and cued attention tasks. The model will find important application in identifying the effects of neural perturbations (stimulation or inactivation) on an animal's perception in multialternative attention and decision-making tasks.