Christopher L. Stitt

The Role of Small Changes in the Acoustic Environment in Modifying the Startle Reflex.

When either the intensity or frequency spectrum of an approximately 70-db. SPL narrow-band noise was abruptly changed by a small amount, the rats response to a startle stimulus presented 64 msec later was inhibited. When similar small frequency changes preceded the startle stimulus by ony 5 msec, the latency of the startle response was reduced, but even relatively large changes in intensity of the antecedent stimulus had no effect on response latency. These findings provide added support for the generalization that the neural processes associated with startle are engaged by small changes in the auditory environment. They also point to a measure of separation between the processes responsible for inhibition and those responsible for latency shift.

Interaction Versus Independence of Startle-Modification Processes in the Rat.

In a series of experiments it was found that the amount of inhibition produced by a weak acoustic stimulus occurring 64 msec prior to a startle-eliciting stimulus is unaffected by a second weak acoustic stimulus occurring 4 msec prior to the startle-eliciting stimulus. Likewise, the amount of latency reduction produced by an antecedent stimulus with a 4-msec lead time is unaffected by the presence of an antecedent stimulus with a 64-msec lead time. Finally, it was found that both the amount of inhibition produced by a prestimulus with a 64-msec lead time and the amount of latency reduction produced by a prestimulus with a 4-msec lead time are independent of the intensity of the startle-eliciting stimulus. These findings suggest that the inhibition effect is independent of the latency reduction effect and that both are independent of the absolute level of activation in the neural mechanisms responsible for the overt startle response.

Reflex inhibition audiometry. A new objective technique.

The reflexive eyeblink, elicited by a tactile stimulus, is inhibited if an auditory stimulus precedes the eliciting stimulus by 100 msec. With adult subjects the threshold for this effect was found to be sufficiently low to suggest that reflex inhibition may be useful in objective audiometry. A preliminary investigation with infants and children showed that the inhibitory process is present, though variable, in children as young as 6 weeks olds.

Modification of the rat's acoustic startle response by antecedent visual stimulation.

Male hooded and albino rats were exposed to a light flash followed at various temporal intervals by a startle-eliciting 117 db. (re 20 muN/m2) burst of white noise. The visual stimulus engendered startle response inhibition (maximally when the lead time was 64-250 msec) as well as startle response latency reduction (maximally when the lead time was 2-8 msec). The temporal functions for the effects of visual stimuli paralleled those previously reported for startle modification by acoustic events. Further study revealed that, given optimal lead times, inhibition is produced reliably by weaker visual stimuli (3 X 10-6 cd-sec/cm2) than latency reduction (3 X 10-4 cd-sec/cm2). This differential sensitivity to visual stimuli is also analogous to previously reported findings for events in the acoustic environment. It reveals that the neural mechanisms that mediate latency reduction and inhibition can be engaged by either acoustic or visual stimulation.

Acoustic augmentation and inhibition of the human eyeblink

The human eyeblink elicited by a mechanically produced tap to the glabella was inhibited by a mild acoustic stimulus presented 200 msec prior to the tap and was augmented when the same acoustic stimulus was presented simultaneously with the tap. Monaural presentation of the acoustic stimulus prior to the tap yielded more reflex inhibition than when that same stimulus was presented binaurally. Binaural presentation of the acoustic stimulus simultaneously with the tap yielded more reflex augmentation than when that same stimulus was presented monaurally. These findings lend credence to the proposition that reflex inhibition and reflex augmentation are mediated by separate neural pathways.

Group shift to caution at the race track

Abstract Group and individual riskiness were compared on

Inhibition of the glabella reflex by monaural and binaural stimulation.

2 “win” best at the race track. Using the standard pretest-posttest risk-shift design, group discussion to unanimous decision was found to produce a cautious shift in group bets.

Stereotyping: From prejudice to prediction.

The human eyeblink, elicited by a tap to the glabella, can be inhibited if a relatively weak acoustic signal precedes the tap by approximately 100 msec. The work reported here was designed to explore the surprising fact that more inhibition occurs when the acoustic prestimulation is presented monaurally than when it is presented binaurally. The present studies revealed that (a) given equally loud binaural inputs, a reduction of about 40 dB(A) in one of them is sufficient to produce inhibition comparable to that produced by a monaural signal, (b) the difference between nonaural and binaural inhibition remains constant as the intensity of prestimulation is varied, and (c) the simultaneous offset of a tone in one ear and onset of a tone in the other ear produces more inhibition than either monaural offest or onset alone. These findings suggest that the specific attributes of a given acoustic signal make independent contributions to the inhibition produced by that signal.