Effects of motor activity on the elicitation and modification of the startle reflex in rats

In order to examine the effects of efferent processes on the elicitation and modification of startle behavior, we administered startle-eliciting stimuli to rats while they were engaged in spontaneous motor activity. When tone bursts (Experiment 1) or electric shocks (Experiment 2) were used to elicit the reflex, its amplitude was substantially less when the rats were active than when they were quiet. Grooming, face washing, and consuming were associated with the greatest reduction. The ability of a 50-dB auditory prepulse to inhibit a subsequent auditory startle was also reduced during activity (Experiment 3). The amount of inhibition produced by a prepulse was decreased even when the baseline startle responses were equated in quiet and activity by varying the intensity of the eliciting stimulus, indicating that the reduction was not due to an artificial “floor effect” (Experiment 4). The study demonstrated that both sensory and motor events affect reflexive responses in the rat, as is known for the human.     

Fear potentiation of the acoustic startle reflex using noises of various spectral frequencies as conditioned stimuli

The effectiveness of noise of various intensities and frequencies in modulating the amplitude of the acoustic startle reflex was evaluated, as a preliminary test of the capacity of these noises to produce consistent and reliable fear-potentiated startle in rats. It was determined that bands of noise containing high frequencies (greater than 10 kHz) tend to unconditionally reduce acoustic startle responses, probably by masking the high-frequency startle-eliciting stimulus. Noise containing high frequencies produced reliable fear-potentiated startle only when its estimated unconditioned startle suppression was subtracted from the enhancement obtained after pairing it with footshocks. Noises devoid of high frequencies produced modest-unconditioned startle enhancements and the most robust and reliable fear-potentiated startle when they were paired with footshocks. A nonmonotonic relationship between training shock intensity and the level of fear-potentiated startle was also exhibited when a low-frequency noise was used as a conditioned stimulus, a finding consistent with previous studies in which a visual stimulus was used. Finally, a differential Pavlovian conditioning procedure indicated that rats could readily discriminate between two different low-frequency bands of noise. The outcome of these experiments indicates that it is easier to employ low-frequency bands of noise to obtain auditory fear-potentiated startle with high-frequency startle-eliciting stimuli.     

Persistent effect of noise on the acoustic startle reflex in the rat

Continuous noise facilitates acoustic startle reflexes in the rat. Rats were exposed to noise for 23 h (Experiment 1) or to 23 h of startle eliciting stimuli at the rate of 1/min (Experiment 2). Facilitation was reduced following habituation in Experiment 2, but was unaffected by prolonged noise exposure in Experiment 1. Reflex inhibition produced by a brief noise was not altered by habituation. Prior experiments show that increases in intensity of continuous noise engage two disparate processes which affect the acoustic startle reflex, one facilitatory (arousal) and one inhibitory (masking). The present data reveal that arousal is not diminished by prolonged noise exposure. The loss of facilitation following reflex habituation may be attributed to its increased susceptibility to masking, or to a direct effect of stimulus repetition on the arousal process normally associated with the noise background.     

Fear-potentiated startle using three conditioned stimulus modalities

The capacities of three different conditioned stimulus modalities (light, noise, and airflow produced by a fan) to produce fear-potentiated startle were evaluated. Previous experiments have shown that following either light-shock or noise-shock pairings, both the light and noise conditioned stimuli acquire the ability to potentiate the acoustically elicited startle response in rats (the so-calledfear-potentiated startle effect). In Experiment 1, the ability of airflow produced by a fan to act as a conditioned stimulus was investigated. Rats were given either paired or impaired fan-shock training followed by a test for fear-potentiated startle. The fan conditioned stimulus potentiated startle only in the group given explicit fan-shock pairings. In Experiment 2, we evaluated the discriminability of the three conditioned stimulus modalities. Rats were given light, noise, or fan-shock pairings and were subsequently tested for fear-potentiated startle with the trained conditioned stimulus as well as the two remaining novel conditioned stimuli. Only the trained conditioned stimulus potentiated startle. These results show that fear-potentiated startle can be produced with three discriminable conditioned stimulus modalities, allowing the future use of fear-potentiated startle in the investigation of higher order conditioning phenomena.     

Inhibition of the startle reflex in the rat by prior tactile stimulation

In Experiment 1, three groups of rats received a tactile prepulse 0.5, 1, or 2 mA electric shock (to feet) .25, .5, 1, 5, 10, or 20 sec prior to an acoustic startle stimulus. The startle response was, maximally inhibited at the .25-sec interval and gradually recovered thereafter. Inhibition was larger with the intense stimuli, and for the .5-mA stimulus occurred reliably only in animals which responded to the prestimulus. In Experiment 2, the intensity of the prepulse was varied within subjects at intervals of .5, 1, and 2 sec. Inhibition was directly related to prestimulus intensity and was greatest at .5 sec. In Experiment 3, an EMG measure of startle reactivity allowed the use of shorter intervals. The maximal inhibitory interval between the prestimulus and startle stimulus was 40 msec compared with either a shorter 10-msec or a longer 250-msec separation.     

Dissociation of the blocking of conditioned eyeblink and conditioned fear following a shift in US locus

Two experiments with rabbits investigated the concordance of two measures of conditioning, eyeblink and potentiated startle, during a blocking sequence with paraorbital shock reinforcement. In both, a shift in the locus of shock from one eye to the other between the conditioning of an element and a compound of that element and a new cue had differential effects on the two measures of conditioning to the new cue. When the shock was unchanged, diminished conditioning in relation to controls (i.e., blocking) was observed on both measures. When the shock was changed, little conditioning was observed in startle, but control-equivalent amounts were observed in eyeblink (i.e., blocking occurred on the former but not the latter). The results are interpreted as showing a dissociation of the associative learning involving the emotive features of Pavlovian reinforcers and that involving the remaining sensory-perceptual features, and more compatible with a diminished US-processing, than with a CSprocessing, view of blocking.     

Affective Influences on Startle in Five-Month-Old Infants: Reactions to Facial Expressions of Emotion

Convergent methodologies from studies of fear-potentiated startle in animals and studies of affective modulation of reflex blinks in humans were adapted in order to investigate infants' sensitivity to affective information conveyed by facial expressions of emotion. While 5-month-old infants viewed photographic slides of faces posed in happy, neutral, or angry expressions, a brief acoustic noise burst was presented to elicit the blink component of human startle. Blink size was augmented during the viewing of angry expressions and reduced during happy expressions. Infants did not show marked changes in behavioral reactions to the positive, neutral, and negative slides, although motor activity was slightly reduced during negative slides. Results suggest that, by 5 months, infants react to affective information conveyed by unfamiliar human faces. Potential mechanisms mediating the influence of affective stimuli on reflex excitability are considered.     

Modification of acoustic and nociceptive reflexes in the rat by visual stimulation

Three experiments demonstrated in the rat that the flexor reaction to a nociceptive cutaneous stimulus (a .5-msec, .5-mA electric shock to the feet) was inhibited by a preceding light flash. In the first, the optimal lead time was at 50 or 100 msec compared to separations of 5 or 400 msec. In the second, the inhibitory effect was shown in ambient noise approximating threshold, indicating that the response decrement was not caused because the light may have blocked a facilitating effect of a moderate background noise level. In the third experiment, the light flash inhibited both the flexor reaction to the cutaneous stimulus and to an acoustic startle stimulus with which it was randomly intermixed. These findings reveal that inhibition is not specific to a particular modality of eliciting stimulus input, though it may be restricted to a particular class of motor events, that is, to flexor reactions.     

Signal properties of reinforcement and reinforcement omission on a multiple fixed-ratio schedule

A series of experiments used food-deprived pigeons to examine several parameters of reinforcement omission in an attempt to control changes of keypeck response measures on a subsequent schedule. In Experiments 1 and 2, the pigeons were tested with a multiple fixed-ratio schedule on which reinforcement was occasionally omitted at the completion of the first component. The duration of the delay occurring in lieu of reinforcement was systematically varied. In Experiment 3, the stimulus that signaled the second component of the schedule was altered to appear either more or less similar to the stimulus that signaled the first component. Two principal results are reported: (1) Response latency decreased and, to a much lesser extent, terminal response rate increased as the delay occurring in lieu of reinforcement decreased; and (2) both latency decrease and response-rate increase were enhanced by a second component stimulus which was similar to the first. The results are evaluated in terms of Amsel’s frustration theory and an analysis by Staddon which suggests that reinforcement inhibits responding. The data appear to support Staddon’s argument that rate increases and latency decreases following reinforcement omission are largely a function of an attenuation of the inhibitory influence of reinforcement, an effect that is enhanced by stimulus generalization. Accordingly, it is proposed that an animal’s response to reinforcement omission is determined by a stimulus complex that minimally includes the omission event and component cues.     

Conditioning-specific reflex modification of the rabbit (Oryctolagus cuniculus) nictitating membrane response is sensitive to context

Conditioning-specific reflex modification occurs when an unconditioned response is modified in theabsence of the conditioned stimulus as a result of pairings of the conditioned stimulus and an unconditioned stimulus. In two experiments, we assessed conditioning-specific reflex modification in either a novel context (Experiment 1) or a context different from, but equally familiar in relation to, the training context (Experiment 2). Conditioning-specific reflex modification did not demonstrate sensitivity to a novel context but did demonstrate sensitivity to a change in familiar context. The data cannot be explained by unconditioned stimulus preexposure, overtraining, or context insensitivity. The results suggest that conditioning-specific reflex modification models normal stress and may be used to evaluate theories of and treatments for posttraumatic stress disorder.     

Divergence of conditioned eyeblink and conditioned fear in backward Pavlovian training

Two experiments of Pavlovian conditioning with rabbits evaluated the effects of initiating or continuing a conditioned stimulus (CS) after a paraorbital unconditioned stimulus (US). In Experiment 1, backward pairings, in which a CS came on after the US, produced a CS that appeared inhibitory on a measure of eyeblink conditioning but excitatory on a potentiated-startle measure of conditioned fear. In Experiment 2, extending the duration of a CS that came on prior to the US, so that it continued after the US, decreased eyeblink conditioned responses, whereas it increased conditioned fear. The data from the two experiments confirm and extend those of Tait and Saladin (1986), supporting the suppositions of AESOP (Wagner & Brandon, 1989) that conditioned eyeblink and conditioned fear can be dissociated under various temporal relationships between the CS and US.     

Chemosensory-based contextual conditioning inHermissenda crassicornis

In two experiments, the marine molluskHermissenda crassicornis was exposed to context discrimination training. In one context, defined by the presence of a diffuse chemosensory stimulus (shellfish extract A), brief, unsignaled, unconditioned stimuli (USs; high-speed rotation) were presented; in a second context, defined by the presence of shellfish extract B, no USs were presented. Animals were then tested (at both 1.5 and 24 h) by exposing them to small pieces of the shellfish meat used to define the two contexts. The latency to strike at the meat served as an index of the context-US association. In Experiment 1, the latency to strike at the cue associated with rotation was reduced relative to both preconditioning strike latencies and the associatively neutral cue. However, in a two-choice test where the animals could approach the conditioned or neutral stimulus, the animals regularly avoided the stimulus paired with rotation. Moreover, if, following conditioning, the animals were presented with an unsignaled rotation in the conditioned context or the neutral context, the animals exhibited more effective defensive clinging (an unconditioned reflex normally elicited by rotation) in the conditioned context, suggesting that it “prepared” the animal for the aversive US. In total, these results demonstrate thatHermissenda is capable of making associations to diffuse background (contextual) stimuli. Moreover, the results suggest that pairing the chemosensory cue with an aversive US elicits a strike response inHermissenda when the animal is placed in forced contact with the cue and an active avoidance response when the animal can choose between that cue and a neutral cue.     

Infant Visual Attention and Stimulus Repetition Effects on Object Recognition

This study examined behavioral, heart rate (HR), and event-related potential (ERP) correlates of attention and recognition memory for 4.5-, 6-, and 7.5-month-old infants (N = 45) during stimulus encoding. Attention was utilized as an independent variable using HR measures. The Nc ERP component associated with attention and the late slow wave (LSW) associated with recognition memory were analyzed. The 7.5-month-olds demonstrated a significant reduction in Nc amplitude with stimulus repetition. This reduction in Nc was not found for younger infants. Additionally, infants only demonstrated differential LSW amplitude based on stimulus type on attentive trials as defined by HR changes. These findings indicate that from 4.5 to 7.5 months, infants’ attentional engagement is influenced by an increasingly broader range of stimulus characteristics.     

Effects of US parameters on classical conditioning of cat hindlimb flexion

Unconditioned stimulus (US) intensity and duration were manipulated to determine their effects on cat hindlimb flexion conditioning. Seven consecutive days of acquisition training of a hindlimb flexor response to a tone conditioned stimulus (CS) were followed by 2 days of extinction. Eight animals in each of 12 groups received a 1-, 2-, 3-, or 4-mA, 60-Hz shock delivered to the right hindleg for 25, 50, or 100 msec as the US. Analysis of conditioned-response (CR) frequency indicated that conditioned responding was a positive function of both the intensity and duration of shock, although these variables did not interact with one another. CR latency and amplitude were decreased and increased, respectively, by increases in US intensity. The pattern of results reported here may support a contiguity notion of conditioning, and are discussed in the context of other conditioning preparations.     

Response deprivation and response satiation as determinants of instrumental performance: Some data and theory

Sixteen human subjects were presented with an instrumental task in which pressing a button to produce a visual stimulus was followed by an auditory stimulus. Half of the subjects were assigned to a condition under which pressing the button at the subject’s operant level produced less of the auditory stimulus than the subject would normally choose to receive. For the others, pressing the button at operant level produced more of the auditory stimulus than the subject would choose. Subjects in the former condition showed increases in instrumental performance; those in the latter showed decreases. The results indicated that the rewarding or punishing effects of an event depend upon the relation of the instrumental contingency to the subject’s unconstrained behavior.     

条件反射理论在心理治疗中的应用研究

条件反射理论最早由俄国著名的生理学家巴甫洛夫提出来，称为经典条件反射理论，之后美国心理学家斯金纳又提出了操作性条件反射理论。条件反射对行为的改变具有重要意义，在学校的教学过程中，学生 一些不适当行为可以用强化手段来塑造。利用行为改变技术，通过操纵强化物来改变学生的行为，这是条件反射理论在心理治疗上的意义。     

Reflex inhibition and reflex elicitation by acoustic stimuli differing in abruptness of onset and peak intensity

The rat’s acoustic startle reaction to a loud tone (S2) was inhibited by white-noise preliminary stimuli (S1) varying in rise/decay time (5 and 100 msec) and intensity (70, 80, and 90 dB). The amount of inhibition was linearly related to the intensity of S1 but was unaffected by its rise/ decay time. In contrast, the response directly elicited by S1 was affected by both variables, being greater with greater intensity and with the more abrupt onset. These data reveal that reflex elicitation and reflex inhibition are the products of different neural mechanisms.     

Consummatory response latency and the stimulus-reinforcer relation in autoshaping

Autoshaping procedures with pigeons were used to assess the susceptibility of unconditioned response (UR) activity to Pavlovian relations between stimulus and reinforcer events. Foodpeck latency (a measure of UR activity) was investigated as a function of the interval between stimulus (keylight) and reinforcer (grain) presentations, and of the stimulus-reinforcer contingency, that is, the conditional probabilities of reinforcer delivery in the presence and absence of the stimulus. Four experiments indicated that food-peck latency was sensitive to both manipulations. Generally, conditions that led to higher keypeck rates were associated with shorter latencies. Thus, UR potentiation was demonstrated. However, when the bird’s location prior to grain delivery was fixed by imposing a keypeck-reinforcer contingency, UR potentiation vanished; it then reappeared when the location constraint was removed. Visual observations supported the conclusion that food-peck latency effects were mediated by approach/withdrawal tendencies generated by the stimulus-reinforcer relation. Implications of these results for expectancy theory are discussed.     

Second-order conditioning: The importance of stimulus overlap on second-order trials

Second-order conditioning was examined using the rabbit eyeblink paradigm and the gerbil CER paradigm. Pavlov’s hypothesis that stimulus overlap on second-order trials produces conditioned inhibition and that nonoverlap leads to second-order conditioning was not confirmed. Our results also revealed that the manner in which first-order and second-order trials are intermixed has an important influence on the properties of the second-order CS. A within-session mixture of first- and second-order trials tended to produce second-order conditioning, and a between-session mixture tended to produce conditioned inhibition. Second-order conditioning was more prominent with the gerbil fear response than with the rabbit eyelid response.     

Effect of intertrial interval on variable-interval discrete-trial barpressing

In seven experiments, an effect of the intertriai interval (ITI) duration on barpressing by rats was studied. A stimulus signaled a 15-sec variable-interval trial. The first response after the interval elapsed turned the stimulus off and was rewarded with food. Trials were separated by long (about 300 sec) or short (about 10 sec) ITIs. A within-subjects design established that response rate on trials after long ITIs was lower than that after short ITIs (Experiments 1 and 3–7). The effect was not cumulative (the effect of one and five consecutive short ITIs was the same). Response rate after short and long ITIs was the same when a between-subjects design was used (Experiment 2). Response rate was higher after 160-sec ITIs than after 300-sec ITIs, suggesting that the ITI duration at which all longer ITIs are treated the same (i.e., the upper limit) is greater than 160 sec (Experiment 3). When food, the trial stimulus, a novel stimulus, or a familiar stimulus never paired with food, was presented 10 sec before the next trial during some of the long ITIs, response rate on the next trial was similar to that found after 10-sec ITIs (Experiments 4–6). This similarity suggested that these events could mark the start of the ITI. However, the familiar stimulus did so only when it reliably predicted that the next trial would occur after a short interval. The effect of ITI duration on responding was apparently attributable to response latency. Response latency was greater after long ITIs, but once responding began, it was similar after long and short ITIs (Experiment 7).