Frame of reference for visual perception in young infants during change of body position

The visual and vestibular systems begin functioning early in life. However, it is unclear whether young infants perceive the dynamic world based on the retinal coordinate (egocentric reference frame) or the environmental coordinate (allocentric reference frame) when they encounter incongruence between frames of reference due to changes in body position. In this study, we performed the habituation–dishabituation procedure to assess novelty detection in a visual display, and a change in body position was included between the habituation and dishabituation phases in order to test whether infants dishabituate to the change in stimulus on the retinal or environmental coordinate. Twenty infants aged 3–4 months were placed in the right-side-down position (RSDp) and habituated to an animated human-like character that walked horizontally in the environmental frame of reference. Subsequently, their body position was changed in the roll plane. Ten infants were repositioned to the upright position (UPp) and the rest, to the RSDp after rotation. In the test phase, the displays that were spatially identical to those shown in the habituation phase and 90° rotated displays were alternately presented, and visual preference was examined. The results revealed that infants looked longer at changes in the display on the retinal coordinate than at changes in the display on the environmental coordinate. This suggests that changes in body position from lying to upright produced incongruence of the egocentric and allocentric reference frames for perception of dynamic visual displays and that infants may rely more on the egocentric reference frame.     

Cardiac Orienting to Pulsed and Continuous Auditory Stimulation: A Developmental Study

Pulsed presentations of auditory stimulation have been shown to be particularly effective in eliciting cardiac deceleration (orienting) during earliest infancy. In the present study the processing of pulsed as compared to continuous stimulation was studied developmentally for two infant age groups (13–18 and 26–35 weeks) and one adult group. Ten habituation trials of either a pulsed or a continuous 10-sec tone were followed by 2 dishabituation trials, in which the temporal pattern (continuous vs pulsed) was shifted. The dishabituation data showed that the two kinds of stimulation were discriminated, but the only finding of differential processing relating to the relevance of pulsed stimulation for younger infants was a tendency for infant subjects, unlike adults, to show prolonged orienting to initial presentations of the pulsed tone. For rate of habituation there were no differential effects. Only in the adult group was the response during dishabituation influenced by the direction of change of temporal pattern. Orienting to stimulus offset was observed on initial presentations of the continuous stimulus for the older infant group.     

Development of inter-manual transfer of shape information in infancy

Inter-manual transfer of shape information was studied with habituation/dishabituation procedures in 2- and 6-month-old infants. Both age groups habituated to a shape repeatedly placed in one hand and dishabituated when a new shape was placed in the same hand. Subsequent testing revealed that only the 2-month olds dishabituated when the habituated shape was placed in the opposite hand and that only the 6-month olds dishabituated when a new shape was placed in the opposite hand. These results indicate that inter-manual transfer of hand information occurs by 2-months of age and that inter-manual transfer of shape information emerges between 2 and 6 months of age. The implications of the findings are discussed.     

A Mutant Exhibiting Abnormal Habituation Behavior in Caenorhabditis elegans

The acquisition and retention of information by the nervous system are major processes of learning. Habituation is a simple learning process that occurs during repeated exposure to harmless stimuli. C. elegans is habituated when repeatedly given mechanical stimuli and recover from the habituation when the stimuli are stopped. A habituation abnormal mutant was isolated and assigned to a new gene hab-1 whose mutation causes slow habituation. The hab-1 mutant phenotype is remarkable at short time interval stimuli. However, hab-1 mutant worms show normal dishabituation. Ablations of neurons constituting the neural circuit for mechanical reflexes did not abolish abnormalities caused by the hab-1 mutation.     

Habituation and dishabituation of human salivary response.

Habituation may be relevant for understanding how sensory stimuli influence factors related to ingestive behavior. In the first of three experiments in humans we showed that salivation and hedonic ratings to lemon or lime juice habituated within 10 presentations, and dishabituation of the salivation and hedonic ratings to the original juice were observed after a new juice was presented. Experiment 2 replicated the habituation and decrease in hedonics to lemon juice, and showed both dishabituation and a relative increase in hedonics when chocolate taste, rather than another juice, served as the dishabituating stimulus. In a third experiment we showed a video game, a nontaste stimulus, could serve as a distractor to prevent the development of habituation, as well as a dishabituator after habituation had occurred.     

Effect of visual experience on the habituation of orienting behavior

Orienting behavior elicited by novel visual and auditory stimuli was examined in light-reared (LR) and dark-reared (DR) rats at 30, 60, 90, or 120 days of age. Orienting behavior was assessed by examining the rat's ability to interrupt ongoing licking and perform appropriate head and postural adjustments when apparently moving or stationary light displays or tones were presented. When the lights were first presented to the LR and DR rats, their orienting behavior did not differ at any of the ages examined. However, age and visual experience did influence habituation and recovery of orienting with changes in the light display. The older DR rats habituated with fewer repeated presentations of the light displays than their LR counterparts and did not recover orienting as effectively to all the subsequent changes of the light displays. The younger LR and DR rats did not differ reliably. These results are discussed with regard to the nature of the habituation process for rodents and the relation between visual experience and habituation of attentional responses.     

A mutant exhibiting abnormal habituation behavior in Caenorhabditis elegans

The acquisition and retention of information by the nervous system are major processes of learning. Habituation is a simple learning process that occurs during repeated exposure to harmless stimuli. C. elegans is habituated when repeatedly given mechanical stimuli and recover from the habituation when the stimuli are stopped. A habituation abnormal mutant was isolated and assigned to a new gene hab-1 whose mutation causes slow habituation. The hab-1 mutant phenotype is remarkable at short time interval stimuli. However, hab-1 mutant worms show normal dishabituation. Ablations of neurons constituting the neural circuit for mechanical reflexes did not abolish abnormalities caused by the hab-1 mutation.     

Spatial expectations of young human infants,following passive movement

Three experiments are described that investigate 4.5‐month‐old infants' spatial thinking during passive movement using a task that required no manual or visual search. In these experiments, infants habituated to a display located near one corner of a table. Before the test trial the infants were either moved to the opposite side of the table or they remained in the same position that they held during the habituation trials. Also, between the habituation trials and the test trial, the display was either surreptitiously moved to the diagonally opposite position on the table, or the display remained stationary. The results showed that infants generally dishabituated when the actual (allocentric/objective) location of the display was changed between habituation and test. However, in Experiment 3, in which infants had reduced experience moving around the testing chamber, infants dishabituated to a change in their egocentric spatial relationship to the display. The results of this experiment suggest that experience moving around the testing chamber was a prerequisite for such location constancy. Taken together, the findings presented here indicate that with enough experience, young infants become aware of key spatial relationships in their environment during passive movement. © 2010 Wiley Periodicals, Inc. Dev Psychobiol 53: 23–36, 2011.     

Age, sex and strain comparison of habituation of the startle response in the rat

Habituation and sensitization of the acoustic startle response were studied in young (3 month) and aged (26 month) male and female Fischer 344 rats and in young (3 month) and aged (32 month) male Sprague Dawley rats. Tones were presented on 25 consecutive trials for a session, one session on each of four consecutive days. An air puff stimulus immediately preceded trial 20 on each day to test sensitization. All aged rats demonstrated greater short-term (within session) relative habituation than their younger counterparts. Across sessions, aged male rats of both strains habituated more quickly than younger males. Aged female rats habituated more slowly. Sensitization was more likely to occur in younger rats.     

Age and novelty: event-related potentials to visual stimuli within an auditory oddball--visual detection task.

Age-related change of event-related potentials to novel visual stimuli was investigated while participants attended to both auditory and visual stimulation. Meaningful but irrelevant pictures (novel stimuli) were presented to younger (mean=21.8, range=18-26 years) and older (mean=70.0, range=60-78) participants (10 in each group). The participants were performing an auditory oddball task and counting silently the changes of a visually presented letter. In the younger group novel stimuli elicited a posterior positivity in the 220-255 ms range. This component habituated to the repetition of the same picture. In the older group this component had longer latency, and did not habituate. A later positivity had shorter latency and larger amplitude in the younger group, but this positivity was preceded by a negative component (N2b) only in the elderly. Results show decreased sensitivity to the content of the visual stimuli in an earlier stage of novelty processing in the elderly, and the age-related slowing of both orientation-related and task-related processes.     

Theoretical aspects of the neurobiological integration of memory

Whenever a peripheral structure like the visual system captures information, the input signal reverberates in circuits of neurons, which send it thereafter towards: (a) the motor system, triggering a specific response, evoked by a short-term memory mechanism; and (b) the hippocampus, to produce long-term potentiation or depression. Two different processes regulate short-term memory: (1) Homosynaptic depression that inhibits neurotransmitter release by means of a decrease in Ca++ inflow, and an increase in calmodulin affinity for synaptic vesicles; and (2) Heterosynaptic facilitation that triggers neurotransmitter release, whenever serotonin activates a proteinkinase A. Besides carrying out a brief review on the matter, we support two different physiological explanations with regard to: (a) ion exchange process and the interstitial pH during habituation; and (b) the possibility of a sensitive presynaptic neuron interaction within the habituated reverberant circuit, to trigger dishabituation. We also propose the term 'time-mediated stimulatory action dependent' to name those serotonin receptors that may lead to a rapid or a delayed postsynaptic onset responses.     

Habituation of the Orienting Response in Sleep

This experiment was designed with stimulus parameters deliberately chosen to maximize the probability of observing habituation of the orienting response (OR) in sleep: weak stimulus, short interstimulas interval. with test for both dishabituation and spontaneous recovery, Habituation of finger plethysmograph. heart rate, skin potential. and skin resistance responses was studied in delta sleep and RKM sleep in 46 male undergraduate volunteers. There was significant habituation of both finger plethysmograph and heart rate responses in both delta and REM sleep, as well as dishabituation and spontaneous recovery. None of these effects was observed in the electrodermal measures. Results were compared with other studies of habituation of the OR in sleep, as well as theories of habituation. The authors do not interpret the results as demonstrating learning during steep.     

A comparison of children's performance on two recognition memory tasks: Delayed nonmatch-to-sample versus visual paired-comparison

Although 4- to 6-month-old children have a significant tendency to look at new stimuli in a visual paired-comparison task (VPC), they have difficulty in consistently choosing novel objects in a delayed nonmatch-to-sample task (DNMS). To evaluate which factors could account for this difficulty, we tested human infants (10–107 months) and adults (17–25 years) in a DNMS task while monitoring eye fixations. The results indicated that children at all ages reliably looked at (VPC scores) or chose (DNMS scores) the new stimuli about 60% of the time, indicating that both tasks measure visual recognition memory. A videotape analysis of visual attention revealed that children younger than 22 months, but not older children, spent significanlty more time visually exploring the objects rather than looking at the food reward under it. Although this visual attraction to objects in children younger than 22 months of age may have impaired the formation of stimulus-reinforcer association needed to solve the DNMS task, this was not the case for older children, since beyond 22 months of age children consistently looked at the reward while displacing the objects. These results suggest that other cognitive abilities required by the DNMS task may not be fully functional even in children 22 months and older. © 1993 John Wiley & Sons, Inc.     

Age-Related Increase in Cross-Sensory Noise in Resting and Steady-State Cerebral Perfusion

Behavioral research indicates that healthy aging is accompanied by maintenance of voluntary attentional function in many situations, suggesting older adults are able to use attention to enhance and suppress neural activity. However, other experiments show increased distractibility with age, suggesting a failure of attention. One hypothesis for these apparently conflicting findings is that older adults experience a greater sensory processing load at baseline compared to younger adults. In this situation, older adults might successfully modulate sensory cortical activity relative to a baseline referent condition, but the increased baseline load results in more activity than younger adults after attentional modulation. This hypothesis was tested by comparing average functional brain activity in auditory cortex using quantitative perfusion imaging during resting state and steady-state visual conditions. It was observed that older adults demonstrated greater processing of task-irrelevant auditory background noise than younger adults in both conditions. As expected, auditory activity was attenuated relative to rest during a visually engaging task for both older and younger participants. However, older adults continued to show greater auditory processing than their younger counterparts even after this task modulation. Furthermore, auditory activity during the visual task was predictive of cross-sensory distraction on a behavioral task in older adults. Together, these findings suggest that older adults are more distractible than younger, and the cause of this increased distractibility may lie in baseline brain functioning.     

Habituation and Dishabituation of the Orienting Reaction to Between and Within Trial Changes in Pitch and Loudness

We investigated the effect of between and within trial changes in pitch and loudness on the electrodermal orienting reaction (OR), perceptions of movement, and their interaction. First, following 20 habituation trials (6-s, 80dB, 1000 Hz), four groups of 10 subjects experienced either an increase or a between-trial decrease in pitch (2000 or 500 Hz) or loudness (90 or 70 dB) on the 21st trial. Second, four additional groups of 20 subjects heard 20 tones that, within each 6-s trial, either increased or decreased in pitch (500 to 2000 or 2000 to 500 Hz) or loudness (70 to 90 or 90 to 70 dB). During a dishabituation phase each group was split into halves having a nonchanging tone either increasing or decreasing relative to mean pitch or loudness. After each session subjects rated whether they perceived tones as approaching, retreating, or motionless. Compared with groups experiencing constant stimuli, groups presented tones changing within trials had greater skin conductance responses that habituated slower irrespective of direction of change or its perception. During dishabituation a similar number of subjects dishabituated to a stimulus increase as compared to a decrease irrespective of whether the change was in pitch or loudness. Perceptions of movement treated as an independent variable did not predict habituation or dishabituation of the OR. The results generally support Sokolov, and are discussed in relation to hypotheses presented by Sokolov, O'Gorman, and Bernstein.     

Facilitated habituation: Strychnine dose-response effects on neural and behavioral habituation

The effects of two doses of strychnine sulfate (0.125 mg/kg and 0.500 mg/kg) on mouse neural and behavioral habituation were assessed. Reliable alterations in concurrent neural (spontaneous and evoked) activity and spontaneous behavioral activity were obtained as the result of training.Neural habituation was characterized by higher frequency, lower amplitude EEG activity, reduced hippocampal theta activity, increased amplitudes in early components of visual evoked responses, and transient increases followed by progressive decreases of late component amplitudes of the visual evoked responses. Behavioral habituation appeared as decreased gross activity and changes in mouse orientation to cogent features of the test chamber.Low strychnine doses (0.125 mg/kg) reliably facilitated habituation to light flashes and produced lessened sensitivity to dishabituation stimuli. High strychnine doses (0.500 mg/kg) disrupted habituation and produced heightened sensitivity to dishabituation stimuli.The results were accommodated by a modified dualprocess theory of habituation; single process views of habituation were inadequate. The significance of these results to drug facilitation was discussed in terms of optimal arousal and the mediation of pro- and retroactive influences on learning. The characterization of processes underlying memory storage seems amenable to further clarification using CNS stimulants known to operate on such processes.     

Acetyl-L-carnitine affects nonassociative learning processes in the leech Hirudo medicinalis

Acetyl-L-carnitine is a natural molecule widely distributed in vertebrate and invertebrate nervous system. It is known to have significant effects on neuronal activity playing a role as neuroprotective and anti-nociceptive agent, as well as neuromodulatory factor. About its capability of affecting learning processes the available data are controversial. In the present study, we utilized the simplified model system of the leech Hirudo medicinalis to analyze the effects of acetyl-L-carnitine, assessing whether and how it might affect elementary forms of nonassociative learning processes. In leeches with the head ganglion disconnected from the first segmental ganglion, repetitive application of weak electrical shocks onto the caudal portion of the body wall induces habituation of swim induction whereas brush strokes on the dorsal skin produces sensitization or dishabituation when the nociceptive stimulus is delivered on previously habituated animals. Herein, the effects of different concentrations of acetyl-L-carnitine (2 mM - 0.05 mM) have been tested at different times on both sensitization and dishabituation. The results show that a single treatment of acetyl-L-carnitine blocked the onset of sensitization in a dose- and time-dependent manner. In fact, the most effective concentration able to block this process was 2 mM, which induced its major effects 11 days after the treatment, whereas 0.05 mM was unable to affect the sensitization process at all considered time points. On the contrary, acetyl-L-carnitine did not completely abolish dishabituation at the tested concentrations and at every time point. Finally, acetyl-L-carnitine also impaired the habituation of swim induction, but only 11 days after treatment.     

Effects of "Below-Zero" Habituation on Spontaneous Recovery and Dishabituation of the Orienting Response

Twenty male undergraduate Ss underwent habituation of the skin conductance component of the orienting response to a neutral tone, spontaneous recovery, rehabituation, and dishabituation (habituation, H condition). Another 20 Ss underwent the same procedure, except they received an additional 10 stimulus presentations immediately after initial habituation (extended habituation, EH condition). The EH condition resulted in more (not significant) spontaneous recovery and trials to rehabituation than did the H condition, indicating that such a “below-zero” habituation procedure did not strengthen habituation. There were significant differences between the groups in response to a post-rehabituation buzzer (dishabituating stimulus), and in response to the subsequent re-presentation of the original tone stimulus (dishabituation), the EH group giving larger responses than the H group. These latter results were seen as consonant with both the Sokolov (1963) and Groves and Thompson (1970) approaches to habituation, and were discussed in that context.     

Is the integration of heard and seen speech mandatory for infants?

For adults and children, speech perception can be significantly influenced by watching a speaker's mouth movements. While recent reports suggest that infants may be able to integrate heard and seen speech, the current research demonstrates that integration is neither as strong or consistent in infants as it is in adults. Three habituation experiments were conducted. In Experiment 1, female (but not male) infants showed evidence of an adult pattern of integration following habituation with an audiovisual /bi/ and testing with audio /bi/-visual /vi/ (perceived as /vi/ by adults). The interpretation of integration was supported, but only in part, by Experiment 2. In Experiment 3, infants were habituated to a mismatched audio /bi/-visual /vi/ combination and tested on concordant /bi/-/bi/ versus /vi/-/vi/ displays. Here, only male infants showed evidence of integration. These results suggest that an initial mechanism supports integration, but that integration is not mandatory for young infants.