Authors: Judy Lauter, Lauren Scharff, Lindsey Salmons, JenniferAlexander, and Julie Bonomo
This project was presented as a poster at the SouthwesternPsychological Association 2005
PURPOSE. This study was designed to determine whether attentionalshifts between auditory vs. visual input would be associated withchanges in the Auditory Brainstem Response (ABR). The experimentalhypothesis was that during visual attention, one or more peaks of theABR would exhibit Jacksonian "release" signs, such as earlierlatency, higher amplitude, or increased stability in either latencyor amplitude.
METHODS. ABRs based on standard parameters (clicks presented at23.1/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 (chosento represent the same frequency range as the clicks used for evokingABRs), presented in the field at the same time as the clicks evokingthe ABR were presented through earphones; and 2) different-modality(visual), in which the subject counted the number of times a fixationpoint in the center of a flashing checkerboard pattern (such ascommonly used for evoking Visual Evoked Potentials, VEPs) changedfrom blue to red.
Attention conditions were presented in an ABAB sequence, withorder of blocks counterbalanced across subjects so that half thesubjects were tested in the order Auditory-Visual-Auditory-Visual,while the other half were tested in the opposite order. Sixteen youngadult females served as subjects. Four ABR waveforms were collectedin each test block, to support calculation of four dependentvariables for ABR peaks III and V: median latency, peak-to-valleyamplitude, latency stability, and amplitude stability (followingguidelines from our earlier work, the latter two were expressed asthe 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 ABRpeaks. Each MANOVA included: 1) one between-subject variable, orderof test (two levels: auditory first vs. visual first); and 2) onewithin-subject variable, attention condition (two levels: auditoryvs. visual). There were no significant interactions or main effectsfor either stability measure. For the median latencies, there weresignificant interactions for both peaks, such that latency co-variedwith testing order; there were no main effects for these values. Forthe median amplitudes, there were no significant interactions, butthere was one main effect, a significant difference between theamplitude of peak III during visual as opposed to auditory attention.Specifically, peak-III amplitude was larger during visual than duringauditory attention (F(1,14) = 5.36; p = .0362).
DISCUSSION. This result is in keeping with the experimentalhypothesis that, during directed attention to the visual system, theauditory brainstem would exhibit "release," that is, show earlierlatencies, higher amplitudes, and/or greater stability, compared withauditory attention. The findings are interpreted as supporting theHandshaking Model of Brain Function (Lauter, 1999), which extendsHughlings Jackson's explanation of rostro-caudal effects in the motorsystem, to posit analogous organization in sensory systems.
Acknowledgements: Many thanks to the classmates who participatedin data collection for this project: Meagan Carswell, Lauren Cerione,Brandon Dickerson, Suzanne Draper, Alicia Hardy, Rebecca Hulgan,Shawna Lee, Melissa Nissen, and Reshaunda Strickland.