Stimulus Novelty Research Articles

Dynamics of acoustical evoked potentials on a background of habituation to verbal stimulus in persons with different individual anxiety levels.

Changes in the amplitude and the latencies of peak P300 of acoustical evoked potential on a background of the verbal stimulus novelty loss were used for determination of the brain activity specifity in individuals with various anxiety levels. The increase of the peak P300 latency of acoustical evoked potential on a background of trace processes arising after habituation was determined. This parameter did not depend on an anxiety level. However, the latency change depended on the attentional level to a submitted signal. The peak P300 amplitude in the right temporal cortex field was connected with the anxiety level--there was a growth of amplitude on a habituation background with the low anxious subjects, and with the highly anxious people the changes of this parameter were not observed. The anxiety level has rendered influence to dehabituation reaction. Dehabituation is observed with the low-anxiety subjects.

Wavelet analysis of P3a and P3b.

Target/standard discrimination difficulty and the degree of stimulus "novelty" were manipulated systematically in a three-stimulus odd-ball task to assess how these variables affect target and non-target P300 scalp distributions for visual stimuli. Wavelet transformation (WT) analyses were performed on the non-target (P3a) and target (P3b) ERPs to assay how the underlying electroencephalographic (EEG) activity was affected by both the difficulty and novelty factors. When target/standard discrimination was easy, P300 amplitude was higher for the target than the non-target across all electrode sites, and both demonstrated parietal maximums. In contrast, when target/standard discrimination was difficult, non-target amplitude (P3a) was higher and earlier over the frontal/central electrode sites for both levels of novelty, whereas target amplitude (P3b) was greater parietally and occurred later than the non-target components and was generally unaffected by non-target novelty level. The WT analyses indicated that appreciable theta activity was related to the more novel non-target stimuli; primarily target component delta coefficients were affected by the discrimination difficulty variable. The findings suggest that target/standard discrimination difficulty, rather than stimulus novelty, determines P3a generation for visual stimuli but that the underlying theta oscillations are differentially affected by stimulus novelty. WT analysis methods are discussed along with the theoretical and neurophysiological implications of the findings.

Model of familiarity discrimination in the perirhinal cortex.

Much evidence indicates that recognition memory involves two separable processes, recollection and familiarity discrimination, with familiarity discrimination being dependent on the perirhinal cortex of the temporal lobe. Here, we describe a new neural network model designed to mimic the response patterns of perirhinal neurons that signal information concerning the novelty or familiarity of stimuli. The model achieves very fast and accurate familiarity discrimination while employing biologically plausible parameters and Hebbian learning rules. The fact that the activity patterns of the model's simulated neurons are closely similar to those of neurons recorded from the primate perirhinal cortex indicates that this brain region could discriminate familiarity using principles akin to those of the model. If so, the capacity of the model establishes that the perirhinal cortex alone may discriminate the familiarity of many more stimuli than current neural network models indicate could be recalled (recollected) by all the remaining areas of the cerebral cortex. This efficiency and speed of detecting novelty provides an evolutionary advantage, thereby providing a reason for the existence of a familiarity discrimination network in addition to networks used for recollection.

Stimulus novelty differentially affects attentional allocation in PTSD

Background: This study investigated attentional allocation in 39 Vietnam combat veterans, 25 with and 14 without posttraumatic stress disorder, assessing P300 amplitudes and latencies during both three-tone and novelty “oddball” tasks. Methods: The three-tone oddball task consisted of three stimuli: frequent tones (85%), rare target tones (7.5%), and rare distractor tones (7.5%). The novelty oddball task was identical to the three-tone task except that the rare distractor tones were replaced with nonrepeating novel sounds (7.5%). Results: Combat veterans with posttraumatic stress disorder showed significant P300 amplitude enhancements at frontal sites in response to distracting stimuli during the novelty but not during the three-tone oddball tasks. There were no amplitude differences in target tones during either task. Conclusions: The data suggest that combat veterans with posttraumatic stress disorder demonstrate P300 responses consistent with a heightened orientation response to novel, distracting stimuli. This finding is consistent both with the clinical presentation of the disorder and with theoretical notions that individuals with posttraumatic stress disorder demonstrate information-processing biases towards vague or potentially threatening stimuli.

Psychophysiologic assessment of erectile response and its suppression as a function of stimulus media and previous experience with plethysmography

The present study examined college men's (N = 35) differential ability to suppress sexual arousal as a function of (a) stimulus media (audio‐only vs. audiovisual), (b) experience with the procedure, and (c) novelty of the stimulus material. Further, galvanic skin response (GSR) and finger pulse amplitude (FPA) were examined as possible methods of detecting attempts to suppress sexual arousal. In general, participants were able to reduce substantially their plethysmographically‐assessed erectile response, and these efforts were not significantly detectable through GSR or FPA measurement. Further, neither experience nor stimulus novelty were found to have a significant effect on arousal or the ability to suppress it. Participants were, however, less aroused in response to audio‐only presentations than audiovisual presentations once they were experienced with the procedure. This effect, in combination with participants’ considerable ability to suppress, could result in more false negative conclusions being drawn when audio‐only, versus audiovisual stimulation, is used in sex‐offender plethysmography.

Novelty‐induced increased expression of immediate‐early genes c‐fos and arg 3.1 in the mouse brain

The detection of novel stimuli is a memory-dependent process. The presented stimulus has to be compared with memory contents to judge its novelty. In addition, the novelty of stimuli activates attention-related processes that facilitate memory formation. To determine the involvement of limbic and neocortical brain structures in novelty detection, we exposed mice to a novel gustatory stimulus (0.5% saccharin) added to their drinking fluid. We then compared the novelty-induced expression of the two immediate-early genes (IEGs) c-fos and arg 3.1, with their expression in mice familiarized with the same stimulus or mice not exposed to that stimulus. Exposure to taste novelty increased expression of c-fos and arg 3.1 mRNA in the cingulate cortex and deep layers of the parietal cortex. In addition, c-fos mRNA expression was increased in the amygdala and arg 3.1 mRNA was increased in the dentate gyrus. Expression of c-fos and arg 3.1 was elevated 30 min after the exposure to novelty. For arg 3.1, a second peak of expression was found 4.5 h after presentation of the novel stimulus. Our results indicate that the amygdala, the dentate gyrus, and the cingulate and parietal cortices may be involved in novelty detection and associated cognitive events, and suggest that c-fos and arg 3.1 play distinct roles in these processes. © 1999 John Wiley & Sons, Inc. J Neurobiol 38: 234–246, 1999

Flavor Preferences Conditioned by Intragastric Nutrient Infusions in Rats fed Chow or a Cafeteria Diet

Numerous studies demonstrate that chow-fed rats learn to prefer flavors that are associated with the postingestive effects of nutrients. The rats» limited dietary experience (i.e. only lab chow) may have facilitated preference learning because of the novelty of the training stimuli. This possibility was investigated by comparing nutrient conditioning in rats fed chow or a varied “cafeteria” diet. Rats in Experiment 1 were trained during alternate sessions (30 min/day) to drink two different flavors paired with concurrent intragastric infusions of 16% Polycose or water. Both diet groups displayed similarly strong preferences (89%) for and increased acceptance of the Polycose-paired flavor. A more demanding learning task was used in Experiment 2: new flavors were paired with delayed (15 min) infusions of Polycose or water. The chow and cafeteria groups both showed reduced, but comparable (78%, 77%) preferences for the Polycose-paired flavor. In Experiment 3, new flavors were paired with concurrent infusions of 7·1% corn oil or water. Again, the cafeteria and chow groups developed similar preferences for the nutrient-paired flavor (85%, 78%). Also, both groups preferred the Polycose-paired flavor of Experiment 1 to the oil-paired flavor of Experiment 3 (76%, 78%). These results indicate that dietary variety does not interfere with nutrient-conditioned flavor preference learning in rats.

Novelty-induced increased expression of immediate-early genes c-fos and arg 3.1 in the mouse brain

The detection of novel stimuli is a memory-dependent process. The presented stimulus has to be compared with memory contents to judge its novelty. In addition, the novelty of stimuli activates attention-related processes that facilitate memory formation. To determine the involvement of limbic and neocortical brain structures in novelty detection, we exposed mice to a novel gustatory stimulus (0.5% saccharin) added to their drinking fluid. We then compared the novelty-induced expression of the two immediate-early genes (IEGs) c-fos and arg 3.1, with their expression in mice familiarized with the same stimulus or mice not exposed to that stimulus. Exposure to taste novelty increased expression of c-fos and arg 3.1 mRNA in the cingulate cortex and deep layers of the parietal cortex. In addition, c-fos mRNA expression was increased in the amygdala and arg 3.1 mRNA was increased in the dentate gyrus. Expression of c-fos and arg 3.1 was elevated 30 min after the exposure to novelty. For arg 3.1, a second peak of expression was found 4.5 h after presentation of the novel stimulus. Our results indicate that the amygdala, the dentate gyrus, and the cingulate and parietal cortices may be involved in novelty detection and associated cognitive events, and suggest that c-fos and arg 3.1 play distinct roles in these processes.

P3a and P3b from typical auditory and visual stimuli

Objective: Target/standard discrimination difficulty was manipulated systematically to assess how this variable affects target and nontarget P300 scalp distributions for both auditory and visual stimuli. Design and methods: A 3-stimulus paradigm (target, standard, nontarget) was employed in which subjects ( n=16) responded only to an infrequently occurring target stimulus. The perceptual discrimination difficulty between the target and more frequently occurring standard stimuli was varied as Easy or Difficult in different conditions, while holding the nontarget stimulus properties constant. Results: When target/standard discrimination was Easy, P300 amplitude was larger for the target than the nontarget across all electrode sites, and both demonstrated parietal maximums. In contrast, when target/standard discrimination was Difficult, target amplitude (P3b) was larger parietally and occurred later than nontarget components, whereas nontarget amplitude (P3a) was larger and earlier than the target P300 over the frontal electrode sites. Similar outcomes across task conditions were obtained for both auditory and visual stimuli. Conclusions: The findings suggest that target/standard discrimination difficulty, rather than stimulus novelty, determines P3a generation for both auditory and visual stimulus modalities.

A predictive reinforcement model of dopamine neurons for learning approach behavior.

A neural network model of how dopamine and prefrontal cortex activity guides short- and long-term information processing within the cortico-striatal circuits during reward-related learning of approach behavior is proposed. The model predicts two types of reward-related neuronal responses generated during learning: (1) cell activity signaling errors in the prediction of the expected time of reward delivery and (2) neural activations coding for errors in the prediction of the amount and type of reward or stimulus expectancies. The former type of signal is consistent with the responses of dopaminergic neurons, while the latter signal is consistent with reward expectancy responses reported in the prefrontal cortex. It is shown that a neural network architecture that satisfies the design principles of the adaptive resonance theory of Carpenter and Grossberg (1987) can account for the dopamine responses to novelty, generalization, and discrimination of appetitive and aversive stimuli. These hypotheses are scrutinized via simulations of the model in relation to the delivery of free food outside a task, the timed contingent delivery of appetitive and aversive stimuli, and an asymmetric, instructed delay response task.

Experience-dependent regulation of adult hippocampal neurogenesis: effects of long-term stimulation and stimulus withdrawal.

Exposure to an enriched environment has been shown to cause an increase in neurogenesis in the dentate gyrus of adult mice. In this study we examined how this experience-dependent response in adult hippocampal neurogenesis of C57BL/6 mice is modulated under the conditions of long-term stimulation and of withdrawal from the enriched environment. We found that a group which experienced withdrawal from the enriched environment 3 months earlier, had more than twice as many proliferating cells in the subgranular zone as controls and mice experiencing long-term stimulation. We propose that the greater number of proliferating cells after withdrawal reflects a survival-promoting effect on the dividing neuronal stem and progenitor cells during the earlier period of stimulation. No differences between the groups were observed in the number of surviving progeny or their phenotypes. Therefore, the existence of more dividing cells in the withdrawal group did not translate into a significant net increase in neurogenesis in the absence of continued stimulation. Similarly, the finding in the group experiencing long-term stimulation showing no clear benefit over controls could be interpreted as a diminished efficiency of continued environmental stimuli to elicit a neurogenic response. Thus, we propose as a working hypothesis that: 1) stimulation early in life may preserve the neurogenic potential in the dentate gyrus, and 2) the novelty of complex stimuli rather than simply continued exposure to complex stimuli elicits the environmental effects on adult hippocampal neurogenesis.

The Von Restorff effect in visual object recognition memory in humans and monkeys. The role of frontal/perirhinal interaction.

This study reports the development of a new, modified delayed matching to sample (DMS) visual recognition memory task that controls the relative novelty of test stimuli and can be used in human and nonhuman primates. We report findings from normal humans and unoperated monkeys, as well as three groups of operated monkeys. In the study phase of this modified paradigm, subjects studied lists of two-dimensional visual object stimuli. In the test phase each studied object was presented again, now paired with a new stimulus (a foil), and the subject had to choose the studied item. In some lists one study item (the novel or isolate item) and its associated foil differed from the others (the homogenous items) along one stimulus dimension (color). The critical experimental measure was the comparison of the visual object recognition error rates for isolate and homogenous test items. This task was initially administered to human subjects and unoperated monkeys. Error rates for both groups were reliably lower for isolate than for homogenous stimuli in the same list position (the von Restorff effect). The task was then administered to three groups of monkeys who had selective brain lesions. Monkeys with bilateral lesions of the amygdata and fornix, two structures that have been proposed to play a role in novelty and memory encoding, were similar to normal monkeys in their performance on this task. Two further groups--with disconnection lesions of the perirhinal cortex and either the prefrontal cortex or the magnocellular mediodorsal thalamus--showed no evidence of a von Restorff effect. These findings are not consistent with previous proposals that the hippocampus and amygdala constitute a general novelty processing network. Instead, the results support an interaction between the perirhinal and frontal cortices in the processing of certain kinds of novel information that support visual object recognition memory.

Neural Response during Preference and Memory Judgments for Subliminally Presented Stimuli: A Functional Neuroimaging Study

Preexposing subjects to visual stimuli is sufficient to establish a subsequent preference, even when previous exposure is subliminal, such that explicit recognition is at chance. This influence of previous exposure on preference judgments, known as the "mere exposure effect," is a form of unconscious memory. The present functional neuroimaging study examines the mechanism of this effect. Nine volunteer subjects were studied using functional imaging while making forced choice judgments about abstract stimuli on the basis of either preference or memory. Each judgment type was made under two conditions: under one condition one or the other stimulus had previously been presented subliminally, whereas under the second condition both stimuli were novel. Memory judgments were associated with activation of left frontopolar cortex and parietal areas, whereas preference judgments were associated with activation of medial prefrontal cortex and regions of occipital cortex. The modulation of preference by objective familiarity (implicit memory) was associated with right lateral frontal activation. Significant activation of hippocampal gyrus was seen in response to objective stimulus novelty, regardless of judgment type required. Our data thus demonstrate activations of a memory system independent of recollective experience. Dissociable activations within this system implicate a frontopolar involvement in explicit retrieval attempt and right lateral prefrontal cortex involvement in implicit memory expressed in preference judgments. Furthermore, the results suggest that hippocampal response to stimulus novelty can be independent of conscious reportability of familiarity.

Perceptual Constraints on Infant Memory Retrieval

In three experiments with 78 3-month-olds, we asked what determines whether or not a stimulus will pop out and cue retrieval from long-term memory. All infants were trained with mobiles displaying either Qs (feature-present stimuli) or Os (feature-absent stimuli) and were tested 24 h later. When the diagonal line of the Q bisected its rim, feature-absent stimuli controlled retrieval in tests with homogeneous displays, and stimulus novelty controlled retrieval in tests with pop-out displays. A follow-up experiment revealed that the similarity between Q and O determined whether or not Q popped out: When its tail projected externally from the rim, Q popped out and cued retrieval, but O did not (search asymmetry). When its tail projected internally from the rim, however, 3-month-olds failed to discriminate Q from O (the externality effect). These data reveal that target-distractor similarity constrains whether or not a feature-present stimulus will pop out and cue retrieval.

Differential neuronal encoding of novelty, familiarity and recency in regions of the anterior temporal lobe

Activity of 2072 neurones was recorded in the anterior temporal lobe—in area TE, perirhinal cortex, entorhinal cortex and hippocampus—during performance of a visual recognition task by monkeys. In area TE, perirhinal cortex and entorhinal cortex, 454 neurones (38% of the 1162 visually responsive neurones) responded differentially on the basis of the relative familiarity or recency of presentation of the stimuli; in the hippocampus only one (3% of its 40 visually responsive neurones) did so. The differentially responsive neurones were classified into those signalling information concerning the recency (19%), familiarity (37%) or novelty (38%) of stimuli. For 98% of these neurones a decreased response signalled that stimuli had occurred previously: no large response increments were observed. The mean differential latency of each of these types of neurone was shorter (∼75 ms) in area TE than in the other areas. Examples of each of these types of neurone with memory spans of ∼24 h were found in each region. The mean memory span of recency neurones was significantly longer in perirhinal cortex than area TE. For familiarity neurones a significant mean response decrement took 4–8 min to develop, indicating a slow underlying plastic change, in contrast to the rapid change seen for recency and novelty neurones. The implications of these results are discussed in relation to the neuronal basis of recognition memory.

Environmental control of morphine withdrawal: Context specificity or stimulus novelty?

Past investigations of context-specific morphine withdrawal have demonstrated that when rats are tested while undrugged, withdrawal behaviors are more pronounced in an environment previously paired with drug administration than in an environment previously paired with saline administration (even in rats that have had exposure to only low doses of morphine prior to testing). In these studies, rearing is a commonly used index of morphine withdrawal. Rearing is also an exploratory behavior. The higher levels of rearing displayed in a morphine-paired, compared with a saline-paired, environment may be a manifestation of a tendency to explore this environment, rather than a tendency to display withdrawal symptoms in this environment. We evaluated the extent to which rearing and other measures of morphine withdrawal are displayed in drug-paired, saline-paired, and novel environments. The results suggest that, in some cases, apparent context specificity of morphine withdrawal actually results from novelty-elicited exploration.

Cortico-limbic circuits and novelty: a review of EEG and blood flow data.

Novelty detection is a fundamental capacity of all mammalian nervous systems /64/. The ability to orient to unexpected events is critical for both survival and normal memory function /82/. The mechanisms whereby the brain detects and responds to novelty have become of increasing interest to neuroscientists. A review is provided of human electrophysiological and blood flow data focused on delineating the neural systems engaged by novelty. Electrophysiological recording of event-related potentials (ERPs) has shown that novel stimuli activate a distributed network involving prefrontal and posterior association cortex as well as the hippocampus /4,23,24,32,33,36,86,88/. Activation of this network facilitates subsequent memory for novel events /27/. Neural modeling provides additional support for a prominent role of novelty in normal memory function /43/. Blood flow studies employing PET and fMRI have also begun to define the neural regions activated by novelty. The blood flow data provide converging evidence on the role of the hippocampus and cortical association regions in the processing of novelty /30,66,75,76/. The results of the behavioral, ERP and blood flow research confirm that a distributed neocortical-limbic circuit is activated by stimulus novelty. These distributed circuits maintain a template of the recent past /74/. Deviations from the template activate a neocortical-limbic network facilitating behavioral response to and memory storage of novel events.

Auditory–visual Intermodel Matching by a Chimpanzee (Pan troglodytes)

Auditory–visual intermodel information processing was studied in a female chimpanzee. Following the presentation of a recorded sound, the subject had to select, from two alternatives, a photograph that corresponded to the sample sound. Various human voices and sounds produced with objects served as auditory sample stimuli. Photographs of speakers or the sound sources of auditory stimuli served as visual comparison stimuli. When the choice alternatives consisted of a picture of a human and an object, the subject showed a generalization of performance, even when the particular auditory and visual stimuli were presented for the first time. The matching performance of the subject was significantly better when novel stimuli were presented as sample or comparison stimuli than when the trial consisted of familiar stimuli. This suggested that the novelty of stimuli facilitated the subject's performance. In sum, the chimpanzee learned to match an auditory stimulus to the comparison visual stimulus, but intermodel processing was characterized by the deterioration of matching performance with familiar stimuli.

Single Neuron Activity in Human Hippocampus and Amygdala during Recognition of Faces and Objects

The hippocampus and its associated structures play a key role in human memory, yet the underlying neuronal mechanisms remain unknown. Here, we report that during encoding and recognition, single neurons in the medial temporal lobe discriminated faces from inanimate objects. Some units responded selectively to specific emotional expressions or to conjunctions of facial expression and gender. Such units were especially prevalent during recognition, and the responses depended on stimulus novelty or familiarity. Traces of exposure to faces or objects were found a few seconds after stimulus removal as well as 10 hr later. Some neurons maintained a record of previous stimulus presentation that was more accurate than the person's conscious recollection. We propose that the human medial temporal lobe constructs a “cognitive map” of stimulus attributes comparable to the map of the spatial environment described in the rodent hippocampus.

The Effects of CS−Preexposure in Conditioned Taste Aversion: Enhanced Flavor Discrimination

Discrimination between two similar flavors in a conditioned taste aversion situation is generally difficult to establish due to generalization of aversion from conditioned stimuli to stimuli not paired with illness. The findings of experiment 1 demonstrate that this general difficulty may be overcome by preexposing subjects to a similar but non-target flavor prior to conditioning (the CS−Effect). Experiment 2 provided evidence that even limited experience with the CS−(one preexposure prior to conditioning) is sufficient to facilitate stimulus discrimination. Investigations of delay interval effects indicated that the CS−Effect is maintained when 14 days are inserted between conditioning and test (experiment 3) and when 10 days are inserted between preexposure and conditioning (experiment 4). An alternate interpretation of these results in terms of relative novelty of stimuli is discussed.