Howard S. Hoffman

Acoustic and temporal factors in the evocation of startle.

Several acoustic and temporal variables responsible for the elicitation of the rats startle reaction were examined by measuring the subjects overt movement under each of a variety of stimulus conditions. When startle was repeatedly evoked, the response decreased in amplitude, but adaptation was slow and was not complete after 675 stimulus presentations. The threshold for startle evocation increased with repeated stimulation, but partial recovery occurred during interpolated rest periods. Startle reactions were amplified when testing occurred in a background of steady noise, but the effect was independent of the frequency components of the background stimulation. Moreover, although a relatively weak signal could inhibit the reaction to a subsequently presented intense signal, the effect was independent of the frequency characteristics of either signal. Finally, it was found that relatively weak signals could either inhibit the startle reaction to a subsequently presented intense signal or reduce response...

Role of Weak Signals in Acoustic Startle

When a relatively weak pulse of noise precedes an intense (startle eliciting) stimulus by 5 msec, the latency of the rats startle reaction to the intense signal is reduced. When, however, the same pulse of noise precedes the intense stimulus by 150 msec, the startle response to the intense stimulus is inhibited. The present research examined the thresholds for these effects using stimulus configurations in which the weak pulse had intensities as low as 10 dB (re 0.0002 dyn/cm2). Both response inhibition and latency reduction were detected when the weak signal had an intensity of only 35 dB, and the magnitude of the two effects increased with increases in pulse intensity. Since, for signals comparable to the pulses used here, the rats threshold for hearing is approximately 35 dB, it is concluded that the brain system that mediates these effects is probably as sensitive as the auditory system itself.

Startle Reaction: Modification by Background Acoustic Stimulation

Six rats were exposed to a sequence of gunshot-like acoustical bursts during silence, during steady noise, and during pulsed noise. Assessment of their startle reactions to the bursts revealed that a background of steady noise enhanced the response, whereas a background of pulsed noise produced suppression of response. It is hypothesized that pulsed noise causes a relative refractory state in the mechanisms responsible for startle and that steady noise may enhance startle by masking uncontrolled punctiform acoustic stimuli.

Effect of Third‐Formant Transitions on the Perception of the Voiced Stop Consonants

The pattern playback was used to generate synthetic syllables consisting of a wide range of second‐ and third‐formant transitions in initial position with the vowels i and ae. It was found that third‐formant transitions affected the perception of the stop consonants. (The effects of the second‐formant transitions were as previously reported.) When the third formants and their associated transitions were added at the frequency levels appropriate to each of the two vowels, positive transitions strengthened the perception of d at the expense of b or g, while negative transitions had the opposite effect. There was some evidence that variations of the steady‐state level of the third formant changed the effect of a given third‐formant transition. The results suggest that the effect of third‐formant transitions is largely independent of the second‐formant transitions with which they are combined. (This work was supported in part by the Carnegie Corporation of New York, and in part by the Department of Defense in...

Temporal Parameters in Startle Facilitation by Steady Background Signals

When an intense acoustic stimulus is presented to the rat in a background of steady random noise, the startle reaction is larger than when the same stimulus is presented against a background of silence. Two experiments examined the temporal parameters of this facilitation effect. The initial experiment sought to determine how long the background signal must be present before facilitation can be detected. The second experiment examined the question of how long facilitation persists following termination of a background signal. Results indicated that 100 msec of exposure to a background signal is adequate for full development of the facilitation effect, and that the effect exhibits a significant decline by no more than 8 msec after the termination of a background signal.

Enhanced Distress Vocalization through Selective Reinforcement

Eighteen Peking ducklings were imprinted and tested for their tendency to emit distress calls during the presentation and withdrawal of the imprinted stimulus. A subsequent arrangement in which each distress vocalization led to a 5-second presentation of the imprinted stimulus resulted in an enhanced tendency to emit distress calls.

Study of Some Cues in the Perception of the Voiced Stop Consonants

Previous research involving synthetic speech reveals that both the second‐ and the third‐formant transitions play a role in the perception of the voiced stops, |b|, |d|, and |g|. The present experiment examined an additional cue (burst frequency), repeated a portion of the previous research, and collected more information about how the cues act in various combinations.Synthetic speech sounds containing one cue, all possible combinations of two cues, and all possible combinations of three cues were tested on a large group of listeners.Burst frequency was found to act as a cue for the perception of the voiced stops in much the same manner as this variable affects the perception of the unvoiced stops. To the extent that the present experiment overlapped previous research, the two sets of findings were in very close agreement. When cues were combined, they shared in the control of perception in such a way that the contribution of any one cue was largely independent of the nature and the number of the other cu...

The control of distress vocalization by an imprinted stimulus.

Twenty two newly hatched ducklings (A. platyrhynchos) were either exposed to a moving imprinting stimulus under one of several experimental conditions or exposed to an empty stimulus compartment. During these procedures special equipment was used to record distress calls. Ss individually exposed to a moving stimulus emitted first more and then fewer distress calls than Ss individually exposed to an empty stimulus compartment. Ss individually exposed to the moving stimulus while in their cages emitted distress calls whenever the stimulus disappeared from the visual field, but not otherwise. Ss exposed to the moving stimulus while in the company of other Ss failed to emit distress calls during the imprinting procedures. In subsequent tests for the effects of the several procedures the imprinting stimulus was periodically presented and withdrawn. It was found that when tested in isolation: 1. Regardless of the conditions during imprinting procedures, Ss previously exposed to the moving stimulus emitted distress calls when the imprinted stimulus was withdrawn, but they seldom emitted distress calls when the stimulus was present. In general, Ss that had been exposed to the moving stimulus while in their cages (i.e., with subject movement restricted) as well as Ss that had been exposed to the stimulus in the company of other Ss displayed the same vocalization pattern as Ss that had been exposed to the stimulus in isolation. These findings indicated that neither freedom to move about nor social isolation during exposure to an imprinting stimulus are necessary conditions for the imprinting stimulus to acquire control over Ss distress calls. 2. Ss previously exposed to an empty stimulus compartment emitted more distress calls in the presence of the imprinted stimulus than in its absence. This implied that prior exposure to an imprinting stimulus was a necessary condition for stimulus withdrawal subsequently to evoke distress calls. 3. Additional tests were concerned with the factors that played a role in the behavioral control exhibited by the imprinted stimulus. For example, in the previous tests during stimulus withdrawal the imprinted stimulus was stationary and hence silent. In Test 3, during periods of stimulus withdrawal the stimulus continued to move under conditions in which S could hear but not see it. As in the initial tests, Ss emitted many distress calls during stimulus withdrawal, but they emitted very few calls during stimulus presentation. This finding suggested that distress vocalization was primarily under the control of visual rather than auditory stimulation. Test 4 examined the effects of stimulus presentation and withdrawal when Ss were in their own cages versus out of them during testing. More distress calls were emitted when Ss cages were removed than when Ss were tested while in their cages. This finding suggested that in part, the control over vocalization exerted by the imprinted stimulus was mediated by the familiarity of the stimulus configuration that prevailed at a given time. Test 5 examined the effects of stimulus presentation and withdrawal when S was tested in isolation versus in the company of a second duckling. Withdrawal of the imprinted stimulus yielded many distress calls when S was alone, but not when S was accompanied by a second duckling. This finding suggested that in isolated Ss the high incidence of distress calls in the absence of the imprinted stimulus was a reflectieon of the withdrawal of social stimulation.

Stimulus Generalization of Conditioned Suppression

A tone ending in unavoidable electric shock was periodically presented to pigeons while they pecked a key for food. When pecking was completely disrupted by tone, shock was disconnected, and the training tone and tones having new frequencies were presented. Initially the gradient of generalization was broad; as testing proceeded, however, the gradient narrowed severely.

Punishment by Response-Contingent Withdrawal of an Imprinted Stimulus

Newly hatched ducklinigs were exposed to a moving, imprinted stiulullls; if they followed it, the stimnulus was withdrawn briefly. The tendency to follow gradually declined durinig punishment periods, but it returned to prepunishment amounts whlen punishmnent terminated. This finding attests to the efficacy of withdrawal of reinforcement as a techniquie for behavioral control.