Effect of eye closure, mental concentration, and nonauditory sensory stimulation on the threshold and magnitude of the acoustic reflex.

Acoustic reflex threshold and magnitude were measured for normal-hearing subjects in four experiments under conditions of: (1) tight and relaxed eyelid closure; (2) eyes open and closed in light, focusing on a spot, reading, and solving a visual maze; (3) tactile stimulation; and (4) performing a mental task. Measurements were susceptance change in millimhos for a 220 Hz probe tone. A 1000 Hz pure-tone and broadband noise presented contralaterally were the stimuli. All factors affected reflex results. Eyelid closure enhanced reflex responses with tight closure involving voluntary muscle tension having a greater effect than relaxed closure. Both passive and active visual tasks suppressed the reflex. The mental task resulted in suppression of both reflex threshold and magnitude. Vibrotactile stimulation also resulted in a suppressed reflex. Changes were more pronounced with broadband noise as the reflex eliciting stimulus. Clinical implications are discussed.