Repeated Stimulus Presentations Research Articles

Conspecific calls evoke characteristic cardiac responses in mallard ducklings

The cardiac response of mallard ducklings, Anas platyrhynchos, has a characteristic pattern, which varies according to which of three conspecific calls, or an artificial sound, is presented. Ducklings were played one of four acoustic stimuli, each of which has well-documented behavioural efects: maternal alarm calls, maternal assembly calls, duckling distress calls and a synthetic control stimulus. The evoked changes in heart rate consisted of brief phasic responses to the playbacks of each call type, together with a cumulative (tonic) change with repeated stimulus presentations. The phasic response consisted of an acceleration during the stimulus in every case, but, while all three conspecific calls elicited a profound post-stimulus deceleration, characteristic of an orienting response, the control stimulus did not. Two of the stimuli also had significant tonic effects; the assembly call evoked a prolonged increase in heart rate, while the alarm call caused a prolonged decrease. These tonic changes may be related to the locomotor responses characteristically elicited by maternal calls. When both phasic and tonic changes in heart rate are considered, it is apparent that each of the stimuli elicited a unique response. The cardiac response thus provides an assay of sufficient sensitivity to examine both recognition of species-typical calls and discrimination between conspecific vocalizations.

Reflex modification in the electrodermal system: Conceptual and methodological issues

Reflex modification (RM) is the inhibition or facilitation of a reflex response by a stimulus (S1) occurring prior to a reflex-eliciting stimulus (S2). The present experiment investigated two issues: (1) whether RM may be confounded by orienting generated by changes in the experimental procedure, or habituation generated by repeated stimulus presentations; (2) whether the strength of RM is influenced by repeated pairings of S1 and S2, that is, classical conditioning. Two groups of subjects were given two series of stimulus presentations. Group A received first 10 S2-alone presentations, before 10 S1-S2 presentations. Group B received the stimuli in reversed order, that is, first 10 S1-S2 presentations, and then 10 S2-alone presentations. This design permits a comparison of unconfounded with confounded RM, as well as assessment of influences of learning. The results showed RM to be influenced by orienting caused by changes in the experimental procedure. The strength of RM tended to be gradually reduced as a function of the number of S1-S2 pairings, indicating that the orienting response to S1 habituated across trials. It is concluded that RM may be useful in the objective investigation of more complex cognitive processes.

Selecting the Smoothing Parameter for Estimation of Slowly Changing Evoked Potential Signals

Brain evoked potential (EP) data consist of a true response ("signal") and random background activity ("noise"), which are observed over repeated stimulus presentations ("trials"). A signal that changes slowly from trial to trial can be estimated by smoothing across trials and over time within trials. We present a method for selecting the smoothing parameter by minimizing an estimate of the mean average squared error (MASE). We evaluate the performance of this method using simulated EP data, and apply the method to an example set of real flash evoked potentials.

Developmental Studies of Alertness and Encoding Effects of Stimulus Repetition

The findings reviewed here suggest a broadened view of the stimulus-familiarization effect as one of a general class of phenomena resulting from repetition-induced changes in the processes of alterness and encoding. Cantor's original observation of slowed responding to familiarized stimuli can be attributed on this account to experimental conditions under which the magnitude of alterness decrement is greater than encoding facilitation. Exactly the opposite result can be obtained by arranging conditions so as to highlight the encoding facilitation effect relative to the alterness decrement effect. For example, faster responding to familiarized stimuli has been found under conditions in which (1) the imperative stimulus is preceded by a neutral warning signal or, (2) a delay is imposed between the familiarization and the test phases. Earlier, it was noted that the experimental technique of repeated stimulus presentation is widely used in the study of infant perception, with little concern for the mechanisms responsible for what is generically referred to as habituation. Posner and Rothbart (1980) made a similar observation and suggested, on the basis of Kraut's (1976) results, that Habituation in the infant can be viewed as a reduction in the flow of information from the recognition pathway [encoding] into the alerting system. Input is still processed along the recognition pathway, but its failure to activate the alerting system reduces the availability of the central processor and hence of nonhabitual responses. We have developed a model of attention that accounts for our findings and embodies Posner and Rothbart's general idea. It suggests that both the alertness and the encoding functions must reach separate threshold levels for a correct recognition response. The time required to get to each threshold level is changed as a function of stimulus repetition. Repetition slows alertness "rise time," but it speeds encoding "rise time." In comparing the responses to a familiarized color versus those to a novel color, the model can be seen in Fig. 1a. Because any response must await an appropriate level of alertness, the familiarized stimulus is responded to more slowly than the novel one, even though encoding rise time to the familiarized stimulus if fast. Either a delay between familiarization and test or a warning signal acts to mitigate the effects of familiarization on alertness. Alertness rise time for the familiarized stimulus is similar to that for the novel stimulus, but encoding rise time for the familiarized stimulus is faster than for the novel.(ABSTRACT TRUNCATED AT 400 WORDS)

Long latency auditory evoked potentials

Experiment 1 elicited the P1, N1, P2, and N2 components of the long latency auditory evoked potential (AEP) using a 1000 Hz tone presented at 30, 50, or 70 dB SPL and 1-, 3-, or 5- second inter-stimulus intervals to assess the relative effects of the combination of these variables on component amplitude and latency. Four blocks of 16 tone presentations each were recorded from each subject to determine if changes in the AEP would occur because of short-term habituation. Both stimulus factors interacted significantly in a systematic fashion for the amplitude measures, with increases in latency also associated with increases in intensity and inter-stimulus interval. Only minor changes across the four trial blocks for either the amplitude or latency measures were observed over the various stimulus presentation conditions. Experiment 2 employed the same tone stimulus presented at 50 dB SPL and a 3-second inter-stimulus interval. Eight blocks of 64 trials were recorded from each subject on each day for four days to investigate long-term habituation effects. No substantial changes in any of the component amplitudes or latencies were obtained across the 32 trial blocks. It was concluded that intensity and inter-stimulus interval interact to determine AEP amplitude as well as latency values and that the constituent components do not change appreciably with repeated stimulus presentations, even after several days.

The sleeping rat shows signs of orienting response to neutral stimuli.

ABSTRACTCortical arousal, cardiac response, and body movement to auditory stimuli were studied during slow wave sleep (SWS) of the rat. Rats were exposed to sequences of 10 tone pulses of a frequency of 16 kHz, a sound pressure level of 60dB, and n duration of 2 s (Experiment I) or 10 s (Experiment II). Repeated stimulus presentations permitted the evaluation of short‐term habitation. Similar results were found in both experiments, i.e. habitation of the cortical arousal response and of the phasic cardiac deceleration to stimulus onset and offset. With repeated presentations, cardiac acceleration showed a less regular course than cardiac deceleration and cortical arousal. Subsequently presented tone pulses of 80dB did not result in a recovery of the habituated response. Cardiac deceleration and cortical arousal on the one hand, and cardiac acceleration and motor activity on the other hand, were strongly correlated. The results are compared with human studies.

Sensitization to amphetamine and tolerance to cocaine and phencyclidine stimulation in mice

Amphetamine (1.0–7.0 mg/kg), cocaine (5.0–40.0 mg/kg) and phencyclidine (1.0–7.0 mg/kg) increased acoustic startle responding in mice. These drugs, however, had varying effects on habituation of the startle response after repeated exposure to the auditory stimulus. The primary effect of phencyclidine was to disrupt the habituation process, whereas increased startle responding after cocaine developed without modification of the habituation curve. Amphetamine facilitated acoustic startle at all doses, and after administration of 3.0 mg/kg a significant response sensitization as a function of repeated stimulus presentation was evident. Consistent with previous reports the excitatory effects of cocaine and amphetamine on acoustic startle were blocked by pretreatment with haloperidol. Haloperidol, which decreased startle responding, attenuated the facilitating effects of PCP on acoustic startle as well. Chronic exposure to amphetamine, cocaine and phencyclidine had differential effects on startle responding. The facilitating effects of amphetamine on startle were further enhanced after long-term exposure to the drug and the sensitizing effect of repeated amphetamine exposure was observed only when animals were tested with amphetamine. In contrast, tolerance developed after chronic exposure to both cocaine and phencyclidine, and the response attenuation was evident when animals were tested for acoustic startle after cocaine, amphetamine and phencyclidine.

Effects of naloxone and repeated stimulus presentation on cortical somatosensory evoked potential (SEP) amplitude in the rat

The effects of naloxone (1 mg/kg) and of repeated stimulus presentation were investigated on a cortical somatosensory evoked potential elicited by innocuous stimulation of the spinal trigeminal tract in awake, minimally restrained rats. The amplitude of an early cortical component (9-ms latency) habituated after administration of saline but did not habituate after naloxone. Naloxone also enhanced the response decrement of late somatosensory evoked potential components (60 to 120 ms) produced by repeated stimulation. The amplitude of midlatency components (14 to 50 ms) did not change after administration of saline and repeated stimulus presentation. However, the amplitude of these components increased after administration of naloxone and repeated stimulus presentation.

The habituation of sexual arousal.

The effects of two levels of stimulus intensity (medium and high) and two levels of stimulus variability (varied stimuli and constant stimuli) on the habituation of subjective and physiological sexual arousal were investigated in a 2 X 2 factorial design. Forty male volunteers served as subjects. It was hypothesized that, as compared to constant stimuli, varied stimuli would produce higher rates of response attenuation on indices of sexual arousal. This hypothesis was confirmed for both penile response and a subjective measure of sexual arousal. Second, it was hypothesized that stimuli of medium intensity would produce higher rates of response of attenuation on subjective and physiological indices of sexual arousal than would stimuli of high intensity. This hypothesis was partially confirmed for subjective arousal but was not confirmed for the physiological measure of sexual arousal. These results were interpreted as supporting the notions that sexual arousal to erotic stimuli decreases with repeated stimulus presentations and, since the experimental design properly controlled for physiological fatigue, that a habituation process is involved in this observed decrement. The implications of habituation for sex research are discussed.

Operant conditioning of somatosensory evoked potential (SEP) amplitude in rats. I. Specific changes in SEP amplitude and a naloxone-reversible somatotopically specific change in facial nociception

The aim of this experiment was to investigate possible endogenous opioid modulation of innocuous somatosensory activity. Somatosensory activity was measured by recording cortical somatosensory evoked potential (SEP) and reflex movement amplitude evoked by innocuous electrical stimulation of the spinal trigeminal tract in awake rats. Putative endogenous opioid activity was blocked using the opiate antagonist naloxone (1 mg/kg). The amplitude of midlatency SEP components (14-50 ms latency) increased following administration of naloxone and repeated stimulus presentations. The amplitude of these components decreased following administration of the opiate agonist morphine (3 mg/kg). An early cortical component (10 ms latency) habituated following the administration of saline but did not habituate following naloxone. Naloxone also enhanced habituation of the late SEP components (60-120 ms latency) and reflex movement evoked at higher stimulus intensities. Morphine decreased the amplitude of the early cortical component but had no consistent effect on the amplitude of the late SEP components.

An Alertness Decrement Hypothesis of Response Inhibition to Repeatedly Presented Stimuli

Both inhibitory and facilitative effects of repeated stimulus presentation have been observed. Two-factor theory attributes both kinds of effects to changes in specific components of attention. The theory claims that repeated exposure (a) decreases the alerting capacity of a stimulus and (b) facilitates encoding. The purpose of the present research was to provide further evidence that alertness decrement underlies the inhibitory effects of stimulus repetition. Adults were exposed to 30 presentations of a colored circle prior to performing a choice-reaction time (RT) task on which the targets were the familiarized stimulus and a novel stimulus. A warning signal occurred at one of three intervals prior to target onset. It was predicted from the literature on the temporal characteristics of alertness that the relative speed of responding to the familiarized stimulus would vary as a function of the warning signal-target interval. As predicted, responses to the familiarized stimulus were (a) slower than to the novel stimulus at intervals of 0 and 2,500 ms, but (b) faster than to the novel stimulus at 450 ms. The convergence of these findings with the alertness literature suggests an alertness decrement interpretation of response decrements to repeatedly presented stimuli.

PGO waves in rats in the non-paradoxical sleep states

Experiments were conducted in rats in order to characterize further the occurrence of PGO waves recorded from the region of the locus coeruleus, which were elicited by auditory stimuli. Repeated stimulus presentations at regular interstimulus intervals resulted in a consistent, state-dependent pattern in the occurrence and amplitudes of elicited PGO waves. The probability of eliciting a PGO wave was lowest during paradoxical sleep and highest immediately afterwards. This was followed by a gradual decline in responding during the ensuing period of slow-wave sleep. These results were obtained regardless of at what point in the rats' sleep cycles presentations of the auditory stimuli began. In other experiments, a comparison of elicited PGO waves with the acoustic startle reflex revealed major differences between these 2 responses. PGO waves could be elicited with very low intensity stimuli that were below the threshold for producing a behavioral response, while much louder stimuli were required to elicit a startle. The startle reflex habituated in a linear fashion and did not display state-related changes. It was concluded that elicited PGO waves are an electrophysiological sign of sensory responsiveness, and that their spontaneous appearance during and preceding paradoxical sleep reflects endogenously generated reticular activation.

Blockade by glutamic acid diethyl ester of excitation of nucleus tractus solitarii neurons and vasodepressor responses reflexly elicited by vagal stimulation

We investigated in anesthetized (urethane 1.5 g/kg i.p.), paralyzed and ventilated rats, the effect of the glutamic acid (1-Glu) antagonist, glutamic acid diethyl ester (GDEE), on the excitation of neurons in the nucleus tractus solitarii (NTS), characterized as ‘cardiovascular’ (CV) by their capacity to modify their firing rate in response to vagal stimulation and to baroreceptor stimulation produced by elevating blood pressure by norepinephrine (NE). Using an extracellular recording technique, we analyzed the effect of vagus stimulation on 75 cells in the medulla. Vagal stimulation modified the activity of 60/75 units. Thirty-three of the 60 responsive neurons increased, while 27 decreased their firing rate during vagal stimulation. In 10 cells excited by vagal stimulation: (a) the latency of the first recorded spike varied between 3–6 ms ( x =4.2 ms ); (b) the latency to repeated stimulus presentation was unstable; (c) neuronal activity was increased by baroreceptor stimulation elicited by elevating arterial pressure with NE; (d) all of the cells of this group were located in the dorsal NTS. In all 10 cells, systemic GDEE (180 mg/kg i.v.) reversibly blocked both the evoked spikes and the reflex bradycardia and hypotension induced by electrical stimulation of the vagus. GDEE failed to block the vasodepressor response to electrical stimulation of the trigeminal complex. To demonstrate that GDEE is an 1-Glu antagonist in the NTS, it was found that in 8 cells characterized as cardiovascular, 1-Glu released with a micropump from a multibarrel pipette, increased the neuronal activity. In 70% of these cells, GDEE released by the same method reversibly blocked the excitatory effect of 1-Glu. We conclude that some neurons in the NTS, driven by vagal afferents and baroreceptor stimulation, are blocked by an antagonist of 1-Glu.

Behavioral correlates of dopaminergic unit activity in freely moving cats

Single unit activity of dopaminergic neurons in the substantia nigra was recorded in freely moving cats under a variety of conditions. These neurons displayed their highest discharge rate during active waking (3.68 ± 0.30 spikes/s), which was 20% greater than their discharge rate during quiet waking (3.07 ± 0.20). Although these cells fired somewhat faster during active waking, their activity displayed no correlation with phasic EMG changes, and, in general, their activity showed little relationship to overt behavioral changes. As the cat progressed from quiet waking through slow-wave sleep and REM sleep there was no significant change in either the rate or pattern of firing of dopaminergic neurons. In addition, no correlation was observed between the activity of these neurons and either sleep spindles or PGO waves. These neurons did respond, however, to the repeated presentation of a click or light flash with excitation followed by inhibition, with no evidence of habituation. One of the most impressive changes in dopaminergic unit acttivity was a large decrease in association with orienting responses. This was seen in over 50% of the cells in which this relationship was examined. As the behavioral orientation habituated with repeated stimulus presentation, so did the associated dopaminergic unit suppression. In conclusion, dopaminergic neurons maintain a remarkably constant rate and pattern of firing across a variety of behaviors and states. However, this stability can be dramatically altered under special circumtances, such as during and following orienting responses.

Peeping and attachment to visual and auditory stimuli in day-old chicks

The usefulness of peeping in indexing attachment to visual and auditory stimuli was confirmed in chicks between 18 and 30 h post-hatch. Greater attractiveness of the auditory stimulus was associated with a more marked initial reduction in peeping after auditory stimulus presentation, suggesting a greater attentional impact, and with greater effectiveness in reducing peeping during repeated stimulus presentations. There was no difference between the two stimuli in effects on peeping before or shortly after the initial approach to the stimuli. Of additional interest was the observation of a sharp rise in peeping immediately preceding the increased activity associated with initial approach. The possible relationship between peeping and arousal was considered.

Raphe unit activity in freely moving cats: Correlation with level of behavioral arousal

Dorsal raphe unit activity in freely moving cats showed a slow, rhythmic discharge rate during quiet waking (¯X= 2.82 ± 0.17spikes/sec), and displayed a strong positive correlation with level of behavioral arousal. Presentation of an auditory stimulus during quiet waking resulted in significant increases in unit activity of 112% and 39% during the first sec and first 10 sec after the stimulus, respectively. This effect rapidly habituated with repeated stimulus presentations. During active waking, unit activity was significantly increased by 22% as compared to quiet waking, but there was no correlation between unit activity and gross body movements. Raphe unit activity showed a significant decrease of 17% during drowsiness (first appearance of EEG synchronization) as compared to quiet waking, and then progressive decreases during the early (−34%), middle (−52%) and late (−68%) phases of slow wave sleep. During all phases of slow wave sleep, the occurrence of sleep spindles was frequently associated with a transitory decrease in unit activity. The discharge rate would typically decrease during the few seconds immediately preceding the spindle, remain at this low level during the occurrence of the spindle, and then increase immediately after the spindle. Raphe unit activity showed decreases of 81% during pre-REM (the 60 sec immediately before REM onset) and 98% during REM, as compared to quiet waking. Unit activity reappeared 3.2 sec before the end of REM, with significant increases in unit activity of 83% and 17% during the first sec and first 10 sec of unit activity, respectively, as compared to quiet waking. The results of these studies are discussed in relation to the hypothesis that serotonin may play a modulatory, rather than mediative, role in behavioral and physiological processes.

Involvement of norepinephrine in startle arousal after acute and chronic d-amphetamine administration.

Treatment with d-amphetamine produced a dose-dependent increase in startle amplitude in response to a buzzer. This increase appeared to be a reflection of a sensitization effect, i.e., enhanced responsivity as a function of repeated stimulus presentations. Treatment with alpha-methyl-p-tyrosine, which reduced whole brain concentrations of dopamine (DA) and norepinephrine (NE), or treatment with FLA-63, which reduced only NE, antagonized the effects of d-amphetamine on the startle reflex, suggesting a role of NE in this behavior. Startle amplitude was also reduced following chronic d-amphetamine treatment. The effect of d-amphetamine on startle was found to be independent of changes in drug-induced locomotor excitation. The data of the present investigation, together with earlier reports, suggests that tolerance occurs to those behaviors that involve a noradrenergic component.

Effects of telencephalic lesions on the gill cover response of siamese fighting fish

Gill cover extension, a component of the fighting pattern of Siamese fighting fish, Betta splendens, was observed in 7 telencephalic-lesioned and 7 sham-operated fish during exposure to mirror image and live Betta stimuli. The conspecific stimulus elicited more frequent and longer duration gill cover (operculum) responses than the mirror stimulus. Lesioning decreased the frequency of gill cover responses to both stimuli. The mean duration of the gill cover response was not affected by lesioning and, unlike response rate, did not decrease (habituate) with repeated stimulus presentation. Lesioning reduced the efficiency of food retrieval and tended to reduce activity level. Behavioral changes may be related to the extent of the lesion. Results are discussed in relation to current hypotheses concerning forebrain function.

The effect of intensity on the localization of different acoustical stimuli in the vertical plane

Two experiments have been carried out to investigate the effects of using different stimuli, various intensities, and repeated stimulus presentation on the ability to localize sounds in the vertical plane. It was found that noise can be localized more accurately than a speech stimulus. Increasing the sensation level of the stimulus reduces localizational errors up to a sensation level of 70 dB, where the error appears to reach a plateau at about 3·5°. There is little or no apparent learning process involved in the task of auditory localization.

Neural correlates of habituation and dark adaptation in the visual cortex of the rat

Sixteen rats were chronically implanted with monopolar electrodes over the primary visual cortex. Averaged evoked responses to repetitive flashes of light were evaluated during habituation and dark adaptation at two stimulus intensity levels. It was found that no consistent changes occurred in the early evoked response components if the rats were dark adapted prior to testing. However, significant increases in amplitude of the early components did occur over trials in nondark-adapted rats, with greatest increases occurring with the dimmer of the two stimulus intensities. These data were interpreted as demonstrating that the early evoked response components constitute a neurophysiological analog to psychophysical functions of brightness perception. Contrary to these effects, the later evoked response components were not influenced by dark adaptation. However, significant changes did occur over repeated stimulus presentations which are most easily accounted for by concepts of habituation. Increases as well as decreases in amplitude were observed depending upon the particular component, with the largest and more prolonged effects resulting from stimulation with the less intense light. These characteristic changes in averaged evoked responses support the notion that early and late components represent two different classes of neural events, and support a “stimulus-model” theory of habituation, but are inconsistent with an “afferent-inhibition” theory.