Authors: Judy Lauter, Lauren Scharff, Lindsey Salmons, Jennifer Alexander, and Julie Bonomo
This project was presented as a poster at the Southwestern Psychological Association 2005
PURPOSE. This study was designed to determine whether attentional shifts between auditory vs. visual input would be associated with changes in the Auditory Brainstem Response (ABR). The experimental hypothesis was that during visual attention, one or more peaks of the ABR would exhibit Jacksonian "release" signs, such as earlier latency, higher amplitude, or increased stability in either latency or amplitude.
METHODS. ABRs based on standard parameters (clicks presented at 23.1/sec, 60 dB nHL, etc.) were collected using a Biologic Navigator, under two contrasting attention conditions: 1) same-modality (auditory), in which the subject counted the number of tones (chosen to represent the same frequency range as the clicks used for evoking ABRs), presented in the field at the same time as the clicks evoking the ABR were presented through earphones; and 2) different-modality (visual), in which the subject counted the number of times a fixation point in the center of a flashing checkerboard pattern (such as commonly used for evoking Visual Evoked Potentials, VEPs) changed from blue to red.
Attention conditions were presented in an ABAB sequence, with order of blocks counterbalanced across subjects so that half the subjects were tested in the order Auditory-Visual-Auditory-Visual, while the other half were tested in the opposite order. Sixteen young adult females served as subjects. Four ABR waveforms were collected in each test block, to support calculation of four dependent variables for ABR peaks III and V: median latency, peak-to-valley amplitude, latency stability, and amplitude stability (following guidelines from our earlier work, the latter two were expressed as the Coefficient of Stability -- mean/standard deviation).
RESULTS. Eight separate mixed-design MANOVA tests were conducted, one for each of the four dependent variables for each of the two ABR peaks. Each MANOVA included: 1) one between-subject variable, order of test (two levels: auditory first vs. visual first); and 2) one within-subject variable, attention condition (two levels: auditory vs. visual). There were no significant interactions or main effects for either stability measure. For the median latencies, there were significant interactions for both peaks, such that latency co-varied with testing order; there were no main effects for these values. For the median amplitudes, there were no significant interactions, but there was one main effect, a significant difference between the amplitude of peak III during visual as opposed to auditory attention. Specifically, peak-III amplitude was larger during visual than during auditory attention (F(1,14) = 5.36; p = .0362).
DISCUSSION. This result is in keeping with the experimental hypothesis that, during directed attention to the visual system, the auditory brainstem would exhibit "release," that is, show earlier latencies, higher amplitudes, and/or greater stability, compared with auditory attention. The findings are interpreted as supporting the Handshaking Model of Brain Function (Lauter, 1999), which extends Hughlings Jackson's explanation of rostro-caudal effects in the motor system, to posit analogous organization in sensory systems.
Acknowledgements: Many thanks to the classmates who participated in data collection for this project: Meagan Carswell, Lauren Cerione, Brandon Dickerson, Suzanne Draper, Alicia Hardy, Rebecca Hulgan, Shawna Lee, Melissa Nissen, and Reshaunda Strickland.