BRAIN-STEM FREQUENCY-FOLLOWING AND BEHAVIORAL-RESPONSES DURING SELECTIVE ATTENTION TO PURE-TONE AND MISSING FUNDAMENTAL STIMULI

Reaction time (RT), discrimination sensitivity (d'), and the brainstem frequency-following response (FFR) were recorded in 32 subjects performing a selective attention task. Auditory stimuli were a 400 Hz pure tone and a complex ''missing fundamental'' (MF) presented dichotically to separate ears (channels). In two tasks, infrequent target stimuli were either of lower intensity or greater duration than standard stimuli. Behavioral results showed consistently better performance (faster RTs and higher d' scores) in the duration task, and better overall detection of MF targets. FFR attention effects were evidenced by differing amplitudes in attend and ignore conditions. Amplitudes in the attended channel were larger to MF stimuli in both tasks, and to the tone stimulus in the duration task. Responses to tone in the intensity task, however, were lowest when the channel was attended, perhaps reflecting some property of greater task difficulty. The demonstration of FFR amplitude differences between attended and ignored channels suggests that selective attention can modify brainstem evoked responses in humans.