Stimulus significance effects in habituation of the phasic and tonic orienting reflex

Phasic and tonic measures of electrodermal activity were examined in a simple habituation paradigm, using innocuous visual stimuli. Separate groups were used to investigate the effects of stimulus significance, as manipulated by instructions. One group had no stimulus-related task (indifferent group), while the other was asked to silently count the stimuli to report to the experimenter later (significant group). Prestimulus skin conductance levels were considered as measures of the arousal level at each stimulus presentation, and the subsequent electrodermal responses were taken as the phasic orienting reflex (OR) elicited by each stimulus. Changes in prestimulus arousal were taken as measures of the tonic OR to the experimental series. Marked group differences were found in both phasic and tonic components of the OR. Some, but not all, of the significance effects in the phasic OR were attributable to differences in arousal. The results are discussed in the context of theoretical accounts of the OR.     

Limulus psychophysics: dark adaptation in the ventral eye.

Sudden illumination applied to Limulus produces an unconditioned downward tail movement which is under stimulus control and can be used to measure psychophysical thresholds. The method of constant stimuli was used to measure the behavioral dark-adaptation function mediated by the ventral eye of Limulus. The resulting function has two phases, each of which is rectified when log threshold is made a function of long time in the dark. Under the conditions of the present experiment, the transition between the two phases occurred at 6 min. This psychophysical dark-adaptation function has the same form as an electrophysiologic dark-adaptation function obtained by Fein and DeVoe (using the ventral eye receptor potential as the response). In more complex visual systems such two-phase, dark-adaptation functions would usually be interpreted in terms of screening pigment movements or changes in the neural contributions of different receptor classes, but neither interpretation is appropriate for the ventral eye of Limulus.     

Using habituation in machine learning

Habituation, a decrement in response to a stimulus that is presented repeatedly without ill effect, can be identified in almost all animals. It can also be used in machine learning to provide a variety of different applications, such as novelty detection, recency encoding, and temporal signal pre-processing. This paper examines how habituation can be mathematically modelled, and discusses how well these models fit the revised characteristics of habituation. It then demonstrates how the models can be combined with neural networks in order to realise the various applications. Finally, some simple experimental results are presented that demonstrate the effectiveness of the methods.     

Sex differences in fetal habituation

There is some evidence for sex differences in habituation in the human fetus, but it is unknown whether this is due to differences in central processing (habituation) or in more peripheral processes, sensory or motor, involved in the response. This study examined whether the sex of the fetus influenced auditory habituation at 33 weeks of gestation, and whether this was due to differences in habituation or in the sensory or motor components using a set of four experiments. The first experiment found that female fetuses required significantly fewer stimulus presentations to habituate than males. The second experiment revealed no difference in the spontaneous motor behaviour of male and female fetuses. The third experiment examined auditory intensity thresholds for the stimuli used to habituate the fetus. No differences in thresholds were found between males and females, although there was inter-individual variability in thresholds. A final experiment, using stimuli individualized for that particular fetus' auditory intensity threshold, found that female fetuses habituated faster than males. In combination, the studies reveal that habituation in the human fetus is affected by sex and this is due to a difference in central 'information processing' of the stimuli rather than peripheral aspects of the response. It is argued that male and female fetuses present different neurobehavioural developmental trajectories, with females more advanced at 33 weeks than males. This study suggests that research examining prenatal behaviour should consider the factor of fetal sex. This may be particularly pertinent where there is an intention to use the results diagnostically.     

Ontogenetic dissociation of two classes of habituation.

The rates of decrement of two classes of response (an elicited startle reflex and emitted exploratory behavior) were determined in rats of two different ages (15 and 36 days). The rate of decrement in the startle reflex was not clearly differentiated as a function of age. In contrast, there was no evidence of habituation of exploration in the younger animals, whereas the older rats uniformly showed profound response decrements. This ontogenetic dissociation of the two instances of response decrement indicates that accounts of both instances in terms of a common process called habituation may be unwarranted. In addition, these data, in conjunction with earlier findings, indirectly support the possibility that reflex decrements may be relatively more dependent on brain serotonin whereas decrements in exploration may be more dependent on normal cholinergic activity in brain.     

Orienting reaction habituation in chronic alcoholics

A polygraphic study on resistance to habituation of the somatic (EMG), autonomic (finger plethysmogram, galvanic skin reaction, respiration) and EEG (acoustic-evoked potential and EEG-blocking reaction) components of the orienting reaction elicited by a repetitive auditory stimulus was performed in 67 chronic alcoholics and in 70 matched normal subjects (control group). The study showed a significantly lower resistance to habituation of the orienting reaction in alcoholics than in normal control subjects. The severity of this habituation disturbance depended on the patients’ age, type of alcoholism, alcohol consumption intensity and chronicity, as well as the type of resting EEG.     

Analyses of habituation in Caenorhabditis elegans

Although the nonassociative form of learning, habituation, is often described as the simplest form of learning, remarkably little is known about the cellular processes underlying its behavioral expression. Here, we review research on habituation in the nematode Caenorhabditis elegans that addresses habituation at behavioral, neural circuit, and genetic levels. This work highlights the need to understand the dynamics of a behavior before attempting to determine its underlying mechanism. In many cases knowing the characteristics of a behavior can direct or guide a search for underlying cellular mechanisms. We have highlighted the importance of interstimulus interval (ISI) in both short- and long-term habituation and suggested that different cellular mechanisms might underlie habituation at different ISIs. Like other organisms, C. elegans shows both accumulation of habituation with repeated training blocks and long-term retention of spaced or distributed training, but not for massed training. Exposure to heat shock during the interblock intervals eliminates the long-term memory for habituation but not the accumulation of short-term habituation over blocks of training. Analyses using laser ablation of identified neurons, and of identified mutants have shown that there are multiple sites of plasticity for the response and that glutamate plays a role in long-term retention of habituation training.     

Sex-dependent habituation to novelty in rats

Male and female rats were familiarized with one-half of an exploration box for 30 or 60 minutes. When later tested, females showed higher preferences for the other novel half than males. Females also showed higher levels of rearing and ambulation. No sex differences were evident for grooming, freezing or defecation. The results were interpreted as females having habituated to the forced-exposure novelty of the familiar half of the apparatus more rapidly than males when the familiarization period was relatively short. With a longer period, males would have had more time to reach a similar level of habituation to that attained by females familiarized for 30 minutes. Relationships between novelty preferences and both rearing and ambulation as indices of exploration were also discussed in the light of significant correlations for males only.     

Sex-dependent habituation to novelty in rats

Male and female rats were familiarized with one-half of an exploration box for 30 or 60 minutes. When later tested, females showed higher preferences for the other novel half than males. Females also showed higher levels of rearing and ambulation. No sex differences were evident for grooming, freezing or defecation. The results were interpreted as females having habituated to the forced-exposure novelty of the familiar half of the apparatus more rapidly than males when the familiarization period was relatively short. With a longer period, males would have had more time to reach a similar level of habituation to that attained by females familiarized for 30 minutes. Relationships between novelty preferences and both rearing and ambulation as indices of exploration were also discussed in the light of significant correlations for males only.     

Intertrial intervals and visual habituation in neonates

Eighteen 3-day-old human neonates were shown a 12 by 12 black-white checkerboard target for 45-sec. trials with either a 10-, 20-, or 30-sec. intertrial interval until their visual fixation time decreased to a set criterion for habituation. On subsequent recovery trials, a 2 by 2 black-white checkerboard target received significantly longer fixations from boys in the 10-sec. and girls in the 20-sec. conditions. 30-sec. intervals, however, produced little habituation and recovery. The implications of these findings are discussed.     

Contextual control of long-term habituation in rats

This study examined contextual control of long-term habituation and whether such effects are dependent on the habituating response system. Habituation of the acoustic startle response transferred from the home cage to the testing context, whereas habituation of lick suppression was context specific (Experiments 1 and 2). Contextual control of habituation was demonstrated between 2 experimental contexts for lick suppression to a tone (Experiment 3) and bar-press suppression to a light (Experiment 4). Experiment 5 extinguished habituation of lick suppression and the orienting response to a tone with 27 exposures to the habituation context. Context specificity of both responses also was found. Previous failures to demonstrate contextual control of habituation may be due to the choice of response system and to less sensitive procedures to detect response recovery. The habituation mechanism for startle is independent from the process or processes that underlie habituation in other response systems, but the nature of these mechanisms is not yet known.     

Locus of habituation in the human newborn

There is some controversy concerning the youngest age at which an infant will habituate to a visual stimulus or will prefer a novel to a familiar pattern. One suggestion has been that apparently successful reports of habituation and dishabituation in the newborn baby are attributable to retinal adaptation. This interpretation was tested in two experiments. In both experiments monocular conditions of viewing were used: newborns were habituated with one eye as the 'seeing' eye, and posthabituation novelty preferences investigated with the other eye. Significant preferences were found both for a novel colour (experiment 1) and for a novel shape (experiment 2), which implies that a retinal-adaptation model can be ruled out. It is suggested that the habituation effects and the subsequent novelty preferences found in the experiments are most reasonably interpreted as a function of memory formation, and evidence is presented for the storage of visual experience from birth. The results also demonstrate some form of binocular interaction in the newborn.     

Cardiac deceleration in newborns: habituation, dishabituation, and offset responses.

Twenty healthy, 1–4 day-old infants were selected from a sample of 135 neonates on the basis of alertness during testing. The infants were presented mild intensity colored light with gradual onset and offset while heart rate was monitored. Half the infants received six exposures to blue light followed by two exposures to blue-green light, whereas remaining subjects received colors in reverse order. Stimulus duration was 20 sec and variable periods between stimuli averaged 30 sec. Results of trend analysis of variance of the second-by-second cardiac data indicated that for infants older than the median age, the decelerative responses to both stimulus onset and offset were significant. Further, these subjects' onset decelerations significantly habituated within the six stimulus repetitions and significantly dishabituated with change in the stimulus color. Offset decelerations incremented over habituation trials and decremented with change in stimulus color. Responses of younger subjects were more variable which probably reflects their less complete recovery from the effects of maternal medication and the birth process.