Transformation of a waiting schedule into a temporal regulation schedule (DRRD) by addition of external stimuli in the dog

Waiting schedules do not impose temporal regulation but condition the animal to give the operant response during a given time. At the end of the required delay, a positive discriminative stimulus is presented. The suspension of the response while the discriminative stimulus is being given suspension of the response while the discriminative stimulus is being given is accompanied by reinforcement. The transformation of a waiting schedule into a temporal regulation schedule is generally achieved by suppressing the external facilitating factors or by physically modifying them. Our study reveals that a similar transformation can be achieved in the dog by the addition of a further stimulus. This stimulus, which is physically exactly the same as the excitatory stimulus and which punctuates the waiting period, is randomly introduced into the temporal delay. The absence of reinforcement in response to the added stimulus should force the animal to regulate its behavior in time and the additional negative discriminative stimulus favours the expression of the active nature of the inhibation. The results show that subjects can differentiate their response durations according to stimuli that only differ according to temporal location. Thus this pattern resembles a DRRD schedule. The peak of responses at the time of the inhibition stimulus reveals considerable behavioral conflict : either the response must be maintained or the inhibition suppressed. The positive or negative resolution of this conflict reveals noteworthy aspects of the behavioural inhibition process.     

Temporal differentiation in two strains of small rodents: a wood mouse (Apodemus sylvaticus) and an albino mouse (Mus musculus OF1)

Wood mice (Apodemus sylvaticus) and OF1 albino mice (Mus musculus) were compared over durations ranging from 0.5 to 7 s, using the differential reinforcement of response duration schedule (DRRD) and a 'platform' response, i.e. staying on a small platform for a specified criterion duration to be reinforced. Species-related differences were found for mean response durations, efficiency and the number of trials needed to reach a preset performance criterion. Coefficients of variation of response durations did not differ. Overall, OF1 mice needed more trials than wood mice to reach a temporal criterion. However, over 3-7 s, data from both strains almost fitted the behavioral assumptions of Scalar Timing theory. Performance of mongolian gerbils (Meriones unguiculatus) trained in a similar setting was shown for visual comparison.     

Effect of contingent auditory stimuli on concurrent schedule performance: an alternative punisher to electric shock

This study explored whether load auditory stimuli could be used as functional punishing stimuli in place of electric shock. Three experiments examined the effect of a loud auditory stimulus on rats’ responding maintained by a concurrent reinforcement schedule. In Experiment 1, overall response rate decreased when a concurrent 1.5 s tone presentation schedule was superimposed on the concurrent variable interval (VI) 180-s, VI 180-s reinforcement schedule. On the contrary, response rate increased when a click presentation schedule was added. In Experiment 2, the extent of the response suppression with a 1.5 s tone presentation varied as a function of the frequency of the reinforcement schedule maintaining responses; the leaner the schedule employed, the greater the response suppression. In Experiment 3, response suppression was observed to be inversely related to the duration of the tone; response facilitation was observed when a 3.0-s tone was used. In Experiments 1 and 2, a preference shift towards the alternative with richer reinforcement was observed when the tone schedule was added. In contrast, the preference shifted towards the leaner alternative when the click or longer duration stimulus was used. These results imply that both the type and duration of a loud auditory stimulus, as well as the reinforcement schedule maintaining responses, have a critical role in determining the effect of the stimuli on responding. They also suggest that a loud auditory stimulus can be used as a positive punisher in a choice situation for rats, when the duration of the tone is brief, and the reinforcement schedule maintaining responses is lean.     

Patterned response to odor in single neurones of goldfish olfactory bulb: influence of odor quality and other stimulus parameters

Responses of 75 single units in the goldfish olfactory bulb were analyzed in detail for their relationship to the time-course of the change in odor concentration during each odor stimulus. Odor stimuli were controlled for rise time, duration, and peak concentration by an apparatus developed for the purpose. This apparatus enabled aqueous odor stimuli to be interposed into a constant water stream without changes in flow rate. The time-course of the concentration change within the olfactory sac was inferred from conductivity measurements at the incurrent and excurrent nostrils. Temporal patterns of firing rate elicited by stimuli with relatively slow rising and falling phases could be quite complex combinations of excitation and suppression. Different temporal patterns were produced by different substances at a single concentration in most units. Statistical measures of the temporal pattern of response for a small number of cells at a given concentration were more characteristic of the stimulus substance than any of three measures of magnitude of response. The temporal patterns change when the peak concentration, duration, and rise time of the stimuli are varied. The nature of these changes suggests that the different patterns are due primarily to the combined influence of two factors: (a) a stimulus whose concentration varies over time and (b) a relationship between concentration and impulse frequency which varies from unit to unit. Some units produce patterns suggestive of influence by neural events of long time constant. The importance of temporal patterns in odor quality and odor intensity coding is discussed.     

Sensitivity to reinforcement in successive and delayed discriminations

Pigeons' responses were recorded in successive 15-s subintervals of 60-s components of several multiple variable-interval schedules of food reinforcement. In the standard multiple schedule or successive discrimination, discriminative stimuli were present throughout each component. In the delayed discrimination or memory procedure, red or green stimuli were present in the first 15 s of components and were followed by a white stimulus for the remainder of both components. Ratios of responses in the first 15 s of the two components, where discriminative stimuli were present, were sensitive to ratios of reinforcers obtained in the two components, to the same extent in both multiple and memory procedures. In both procedures, sensitivity to reinforcement decreased systematically over component subintervals, but to a greater extent in the memory procedure where discriminative stimuli were absent. The reduction in sensitivity with time since presentation of prior discriminative stimuli in the memory procedure was therefore influenced by two main factors: delayed stimulus control by the discriminative stimuli presented earlier in the component, and a decrease in sensitivity to reinforcement with increasing time since component alternation.     

Understanding the temporal codes of intra-cellular signals

The health of organisms and cells depends on appropriate responses to diverse internal and external cues, stimuli, or challenges, such as changes in hormone or cytokine levels, or exposure to a pathogen. Cellular responses must be tailored to the identity and intensity of the stimulus and therefore intra-cellular signals must carry information about both. However, signaling mediators often form intricate networks that react to multiple stimuli yet manage to produce stimulus-specific responses. The multi-functionality ('functional pleiotropism') of signaling nodes suggests that biological networks have evolved ways of passing physiologically relevant stimulus information through shared channels. Increasing evidence supports the notion that this is achieved in part through temporal regulation of signaling mediators' activities. The present challenge is to identify the features of temporal activity profile that represent information about a given stimulus and understand how cells read the temporal codes to control their responses.     

Neuronal ensemble bursting in the basal forebrain encodes salience irrespective of valence

Both reward- and punishment-related stimuli are motivationally salient and attract the attention of animals. However, it remains unclear how motivational salience is processed in the brain. Here, we show that both reward- and punishment-predicting stimuli elicited robust bursting of many noncholinergic basal forebrain (BF) neurons in behaving rats. The same BF neurons also responded with similar bursting to primary reinforcement of both valences. Reinforcement responses were modulated by expectation, with surprising reinforcement eliciting stronger BF bursting. We further demonstrate that BF burst firing predicted successful detection of near-threshold stimuli. Together, our results point to the existence of a salience-encoding system independent of stimulus valence. We propose that the encoding of motivational salience by ensemble bursting of noncholinergic BF neurons may improve behavioral performance by affecting the activity of widespread cortical circuits and therefore represents a novel candidate mechanism for top-down attention.     

Phonotactic specificity of the cricketTeleogryllus oceanicus: intensity-dependent selectivity for temporal parameters of the stimulus

Summary We have investigated the effects of alterations of several temporal parameters of auditory stimuli, as well as of stimulus intensity changes, on the attractiveness of these stimuli to femaleTeleogryllus oceanicus, as measured by monitoring sound-elicited flight steering responses. AlthoughT. oceanicus has a rhythmically complex calling song, females are attracted by a simpler model consisting of regularly repeating sound pulses. We have found that the two major temporal features of this model, sound pulse duration and pulse repetition rate, are both important for eliciting phonotactic steering responses.Stimuli with altered temporal features had intensity thresholds indistinguishable from the control stimulus (Fig. 3). The majority of crickets, however, ceased to respond to the altered stimuli when the stimulus intensity was sufficiently increased (Figs. 4–7). In some cases, intensity increases resulted in a reversal of the steering response from positive to negative (Fig. 10). Effects of altered temporal parameters were also apparent at lower stimulus intensities, where the amplitudes of steering responses to stimuli with altered parameters were smaller than those in response to the control stimulus (Figs. 8, 9).We considered the possibility that the cessation of responsiveness to stimuli with altered temporal features was due to a temporal pattern-specific diminution of binaural cues for sound localization at high intensities. Experiments performed with unilaterally deafened crickets (Fig. 11) led us to conclude that this was not the case, and that our findings instead reflect the properties of the song recognition mechanism.Abbreviations UIL upper intensity limit - RAF ratio of abdominal flexion     

Massed and spaced stimulus sequences in dimensional discrimination

In two experiments, pigeons' responding to a visual flicker-rate continuum was established by a maintained generalization procedure. For both experiments, variable-interval reinforcement was available for responses during stimuli from one half of the stimulus continuum while responses during other stimuli were extinguished. The first experiment compared gradients of dimensional stimulus control produced by randomly presented positive and negative stimuli with gradients produced by massed positive and negative stimuli. The second experiment alternated the order of massed stimulus sequences. In both cases, massing of stimulus sequences diminished positive dimensional contrast effects, without seriously disturbing discrimination between positive and negative stimuli. The results indicate that stimulus sequences can have an important role in the production of dimensional contrast effects.     

Temporal threshold and response bias in the discrimination of empty intervals by cats

Cat's differential duration threshold was investigated by the method of limits in a schedule of discrimination of empty durations. The standard stimulus was 4 sec long throughout the experiment. The comparison stimulus was reduced from 10 to 5 sec by 1 sec steps in successive blocks of 5 sessions. Standard and comparison stimuli, delimited by 50 msec auditory signals, were equiprobably distributed, in a random sequential order of presentation in each trial. After a 2 sec delay, an auditory signal indicated that reinforcement was available upon a response on one of two levers. Weber fractions around .25 were obtained. Strong response bias developed in most cats. Some consequences of the inhibition of responding induced by the procedure were considered.     

Subjective Duration Distortions Mirror Neural Repetition Suppression

Background

Subjective duration is strongly influenced by repetition and novelty, such that an oddball stimulus in a stream of repeated stimuli appears to last longer in duration in comparison. We hypothesize that this duration illusion, called the temporal oddball effect, is a result of the difference in expectation between the oddball and the repeated stimuli. Specifically, we conjecture that the repeated stimuli contract in duration as a result of increased predictability; these duration contractions, we suggest, result from decreased neural response amplitude with repetition, known as repetition suppression.

Methodology/Principal Findings

Participants viewed trials consisting of lines presented at a particular orientation (standard stimuli) followed by a line presented at a different orientation (oddball stimulus). We found that the size of the oddball effect correlates with the number of repetitions of the standard stimulus as well as the amount of deviance from the oddball stimulus; both of these results are consistent with a repetition suppression hypothesis. Further, we find that the temporal oddball effect is sensitive to experimental context – that is, the size of the oddball effect for a particular experimental trial is influenced by the range of duration distortions seen in preceding trials.

Conclusions/Significance

Our data suggest that the repetition-related duration contractions causing the oddball effect are a result of neural repetition suppression. More generally, subjective duration may reflect the prediction error associated with a stimulus and, consequently, the efficiency of encoding that stimulus. Additionally, we emphasize that experimental context effects need to be taken into consideration when designing duration-related tasks.     

Serial conditional discrimination and temporal bisection in rats selectively lesioned in the dentate gyrus

In positive serial conditional discrimination, animals respond during a target stimulus when it is preceded by a feature stimulus, but they do not respond when the same target stimulus is presented alone. Moreover, the feature and target stimuli are separated from each other by an empty interval. The present work aimed to investigate if two durations (4 or 16 s) of the same feature stimulus (light) could modulate the operant responses of rats to different levers (A and B) during a 5-s target stimulus (tone). In the present study, lever A was associated with the 4-s light, and lever B was associated with the 16-s light. A 5-s empty interval was included between the light and the tone. In the same training procedure, the rats were also presented with the 5-s tone without the preceding light stimuli. In these trials, the responses were not reinforced. We evaluated the hippocampal involvement of these behavioral processes by selectively lesioning the dentate gyrus with colchicine. Once trained, the rats were submitted to a test using probe trials without reinforcement. They were presented with intermediate durations of the feature stimulus (light) to obtain a temporal bisection curve recorded during the exposure to the target stimuli. The rats from both groups learned to respond with high rates during tones preceded by light and with low rates during tones presented alone, which indicated acquisition of the serial conditional discrimination. The rats were able to discriminate between the 4- and 16-s lights by correctly choosing lever A or B. In the test, the temporal bisection curves from both experimental groups showed a bisection point at the arithmetic mean between 4 and 16 s. Such processes were not impaired by the dentate gyrus lesion. Thus, our results showed that different durations of a feature stimulus could result in conditional properties. However, this processing did not appear to depend on the dentate gyrus alone.     

Recalibration of the Multisensory Temporal Window of Integration Results from Changing Task Demands

The notion of the temporal window of integration, when applied in a multisensory context, refers to the breadth of the interval across which the brain perceives two stimuli from different sensory modalities as synchronous. It maintains a unitary perception of multisensory events despite physical and biophysical timing differences between the senses. The boundaries of the window can be influenced by attention and past sensory experience. Here we examined whether task demands could also influence the multisensory temporal window of integration. We varied the stimulus onset asynchrony between simple, short-lasting auditory and visual stimuli while participants performed two tasks in separate blocks: a temporal order judgment task that required the discrimination of subtle auditory-visual asynchronies, and a reaction time task to the first incoming stimulus irrespective of its sensory modality. We defined the temporal window of integration as the range of stimulus onset asynchronies where performance was below 75% in the temporal order judgment task, as well as the range of stimulus onset asynchronies where responses showed multisensory facilitation (race model violation) in the reaction time task. In 5 of 11 participants, we observed audio-visual stimulus onset asynchronies where reaction time was significantly accelerated (indicating successful integration in this task) while performance was accurate in the temporal order judgment task (indicating successful segregation in that task). This dissociation suggests that in some participants, the boundaries of the temporal window of integration can adaptively recalibrate in order to optimize performance according to specific task demands.     

Expectation modulates neural responses to pleasant and aversive stimuli in primate amygdala

Animals and humans learn to approach and acquire pleasant stimuli and to avoid or defend against aversive ones. However, both pleasant and aversive stimuli can elicit arousal and attention, and their salience or intensity increases when they occur by surprise. Thus, adaptive behavior may require that neural circuits compute both stimulus valence--or value--and intensity. To explore how these computations may be implemented, we examined neural responses in the primate amygdala to unexpected reinforcement during learning. Many amygdala neurons responded differently to reinforcement depending upon whether or not it was expected. In some neurons, this modulation occurred only for rewards or aversive stimuli, but not both. In other neurons, expectation similarly modulated responses to both rewards and punishments. These different neuronal populations may subserve two sorts of processes mediated by the amygdala: those activated by surprising reinforcements of both valences-such as enhanced arousal and attention-and those that are valence-specific, such as fear or reward-seeking behavior.     

Expectation Suppression in Early Visual Cortex Depends on Task Set

Stimulus expectation can modulate neural responses in early sensory cortical regions, with expected stimuli often leading to a reduced neural response. However, it is unclear whether this expectation suppression is an automatic phenomenon or is instead dependent on the type of task a subject is engaged in. To investigate this, human subjects were presented with visual grating stimuli in the periphery that were either predictable or non-predictable while they performed three tasks that differently engaged cognitive resources. In two of the tasks, the predictable stimulus was task-irrelevant and spatial attention was engaged at fixation, with a high load on either perceptual or working memory resources. In the third task, the predictable stimulus was task-relevant, and therefore spatially attended. We observed that expectation suppression is dependent on the cognitive resources engaged by a subjects’ current task. When the grating was task-irrelevant, expectation suppression for predictable items was visible in retinotopically specific areas of early visual cortex (V1-V3) during the perceptual task, but it was abolished when working memory was loaded. When the grating was task-relevant and spatially attended, there was no significant effect of expectation in early visual cortex. These results suggest that expectation suppression is not an automatic phenomenon, but dependent on attentional state and type of available cognitive resources.     

Reversing Stimulus Timing in Visual Conditioning Leads to Memories with Opposite Valence in Drosophila

Animals need to associate different environmental stimuli with each other regardless of whether they temporally overlap or not. Drosophila melanogaster displays olfactory trace conditioning, where an odor is followed by electric shock reinforcement after a temporal gap, leading to conditioned odor avoidance. Reversing the stimulus timing in olfactory conditioning results in the reversal of memory valence such that an odor that follows shock is later on approached (i.e. relief conditioning). Here, we explored the effects of stimulus timing on memory in another sensory modality, using a visual conditioning paradigm. We found that flies form visual memories of opposite valence depending on stimulus timing and can associate a visual stimulus with reinforcement despite being presented with a temporal gap. These results suggest that associative memories with non-overlapping stimuli and the effect of stimulus timing on memory valence are shared across sensory modalities.     

Temporal expectancy in the context of a theory of visual attention

Temporal expectation is expectation with respect to the timing of an event such as the appearance of a certain stimulus. In this paper, temporal expectancy is investigated in the context of the theory of visual attention (TVA), and we begin by summarizing the foundations of this theoretical framework. Next, we present a parametric experiment exploring the effects of temporal expectation on perceptual processing speed in cued single-stimulus letter recognition with unspeeded motor responses. The length of the cue–stimulus foreperiod was exponentially distributed with one of six hazard rates varying between blocks. We hypothesized that this manipulation would result in a distinct temporal expectation in each hazard rate condition. Stimulus exposures were varied such that both the temporal threshold of conscious perception (t₀ ms) and the perceptual processing speed (v letters s⁻¹) could be estimated using TVA. We found that the temporal threshold t₀ was unaffected by temporal expectation, but the perceptual processing speed v was a strikingly linear function of the logarithm of the hazard rate of the stimulus presentation. We argue that the effects on the v values were generated by changes in perceptual biases, suggesting that our perceptual biases are directly related to our temporal expectations.     

White Noise Masks Some Temporal Parameters of the Auditory Localization of Radially Moving Targets

The temporal parameters of the perception of radially moving sound sources partly masked with broadband internalized noise at an intensity of 40, 46, or 52 dB above the hearing threshold have been studied. The threshold of sound duration necessary for identifying the direction of movement of the sound source (75% correct answers) increases from 135 ms in silence to 285 ms at all intensities of continuous noise studied. The minimum duration of the stimulus beginning with which a subsequent increase in duration does not increase the number of correct responses is the same (385 ms) under all conditions of stimulus presentation. Broadband noise of any intensity increases the time of response to stimuli in the range of durations studied. At a noise of 52 dB, which is close to the threshold of full masking, the reaction time is not increased significantly compared to its estimation at a noise of 46 dB. The minimum duration of the stimulus has proved to be the stablest temporal parameter of the perception of movement of a sound source. Changes in the temporal parameters of sound perception at noise levels close to the threshold of full masking are discussed.     

Quantitative analyses of observing and attending

We review recent experiments examining whether simple models of the allocation and persistence of operant behavior are applicable to attending. In one series of experiments, observing responses of pigeons were used as an analog of attending. Maintenance of observing is often attributed to the conditioned reinforcing effects of a food-correlated stimulus (i.e., S+), so these experiments also may inform our understanding of conditioned reinforcement. Rates and allocations of observing were governed by rates of food or S+ delivery in a manner consistent with the matching law. Resistance to change of observing was well described by behavioral momentum theory only when rates of primary reinforcement in the context were considered. Rate and value of S+ deliveries did not affect resistance to change. Thus, persistence of attending to stimuli appears to be governed by primary reinforcement rates in the training context rather than conditioned reinforcing effects of the stimuli. An additional implication of these findings is that conditioned "reinforcers" may affect response rates through some mechanism other than response-strengthening. In a second series of experiments, we examined the applicability of the matching law to the allocation of attending to the elements of compound stimuli in a divided-attention task. The generalized matching law described performance well, and sensitivity to relative reinforcement varied with sample duration. The bias and sensitivity terms of the generalized matching law may provide measures of stimulus-driven and goal-driven control of divided attention. Further application of theories of operant behavior to performance on attention tasks may provide insights into what is referred to variously as endogenous, top-down, or goal-directed control of attention.