Developing auditory stimulus control: A note on methodology

This paper concerns the problem of teaching people with intellectual handicaps to respond reliably to spoken words and other auditory instructional stimuli. We describe how microcomputer technology can be applied to implement effective auditory stimulus control shaping methods. With hardware and software currently available, it is now possible to adapt procedures that have been previously successful in stimulus control programming with visual stimuli. We describe several techniques for programming gradual stimulus changes (e.g., stimulus fading, stimulus shaping) to promote auditory discrimination learning. Teaching studies with two individuals with severe mental retardation provide illustrative applications and data supporting the feasibility and potential utility of auditory stimulus control shaping methodology.     

Animal psychophysics: improvements in the tracking method.

It is difficult to maintain stimulus control in animal psychophysical studies using the tracking method. Loss of stimulus control is characterized by wandering thresholds and responses in the absence of the stimulus. Rats were trained to make a variable number of licking responses to turn on an auditory stimulus. A response on a lever in the presence of the stimulus was reinforced with food. Two precedures were added to improve stimulus control. First, lever responses in the absence of the stimulus raised the intensity of the stimulus at the next presentation; second, rate of reinforcement in the threshold region was maintained at about the same level as that in the suprathreshold region by reducing the number of licking responses required to turn on the stimulus. Using these two procedures, stimulus control was improved and maintained and reliable auditory intensity thresholds were obtained.     

Foreperiod and visual stimulus intensity: A reappraisal

The joint effects of stimulus modality, stimulus intensity, and foreperiod on simple RT were investigated. In experiment 1 an interaction was found between stimulus intensity, both visual and auditory, and a variable FP such that the intensity-effect on RT was largest at the shortest FP. Experiment 2 provided a successful replication with smaller and weaker visual stimuli. No interaction was observed with a constant FP, although the visual stimuli were identical and the auditory ones psychophysically equivalent to the visual stimuli of experiment 1.It is proposed that an additive or interactive relationship between stimulus intensity and FP can be inferred only when the mental processes called for by the various uses of FP are simultaneously considered. Another precondition is an adequate sampling of the intensity-continuum with special reference to the retinal size of visual stimuli.     

Simultaneous auditory discrimination.

Stimuli in many visual stimulus control studies typically are presented simultaneously; in contrast the stimuli in auditory discrimination studies are presented successively. Many everyday auditory stimuli that control responding occur simultaneously. This suggests that simultaneous auditory discriminations should be readily acquired. The purpose of the present experiment was to train rats in a simultaneous auditory discrimination. The apparatus consisted of a cage with two response levers mounted on one wall and a speaker mounted adjacent to each lever. A feeder was mounted on the opposite wall. In a go-right/go-left procedure, two stimuli were presented on each trial, a wide-band noise burst through one speaker and a 2-kHz complex signal through the other. The stimuli alternated randomly from side to side across trials, and the stimulus correlated with reinforcement for presses varied across subjects. The rats acquired the discrimination in 400 to 700 trials, and no response position preference developed during acquisition. The ease with which the simultaneous discrimination was acquired suggests that procedures, such as matching to sample, that require simultaneous presentation of stimuli can be used with auditory stimuli in animals having poor vision.     

Establishing stimulus equivalences among retarded adolescents.

Two separate sets of stimuli were established as stimulus classes in a match-to-sample task by using each stimulus as both a sample and choice stimulus for every other member within that set. After classes were established, the subjects were taught to select one member of each class when an associated auditory stimulus was presented. After this training, three of six subjects were able to select the remaining members of each stimulus class in response to the appropriate auditory stimuli without direct training. The other three subjects also demonstrated transfer after additional members of each stimulus class were brought under the control of the auditory stimuli through direct training.     

A programmable multiple-tone generator

A simple tone generator that allows software control of auditory stimuli is described. The circuit provides for the simultaneous generation, timing, and amplification of three different tones. Its low cost, ease of construction, and versatility make it an attractive alternative to conventional auditory stimulus hardware.     

Auditory specific fear conditioning results in increased levels of synaptophysin in the basolateral amygdala

Auditory fear conditioning is one of the most well characterized models used in studies of learning and memory. In order to ensure the animals have been conditioned to fear the auditory stimulus, animals are generally tested for their response to this stimulus in a different context to that used for training. For this reason it is often unclear how much contextual fear conditioning the animals also acquire when they are trained. In this study, we have established a protocol for fear conditioning in mice which is explicit for auditory cues; mice trained using this protocol, show a very low fear response to contextual cues encountered during training. We have undertaken analysis to look for potential brain changes associated with this model by measuring levels of the synaptic vesicle protein, synaptophysin, in the basolateral nuclei of the amygdala following auditory fear conditioning. Our results show levels of synaptophysin were significantly higher in mice which learnt to associate the auditory stimulus with fear, in comparison to all non-learning control animals. These findings support the idea that synaptic plasticity associated with formation of fear conditioning to a single specific conditioned stimulus occurs within the basolateral nuclei of the amygdala. Furthermore, our results demonstrate the usefulness of this model in looking for changes in the brain specific for a defined learning event.     

Stimulus control of heart rate by auditory frequency and auditory pattern in pigeons

A new method was used to investigate auditory discrimination in pigeons. Basically, the method involves the repeated presentation of one stimulus preceding the single presentation of a different stimulus that is followed by shock. Stimulus control is assessed by the increase in heart rate that accompanies the presentation of the second stimulus. In Experiment 1, the efficiency of the method was explored by determining the frequency difference thresholds of pigeons at 500, 1000, 2000, and 4000 Hz. Weber fractions comparable to those reported in an earlier study using the conditioned suppression method were obtained. Experiment 2 demonstrated that, contrary to results of earlier studies, auditory temporal patterns can exercise differential stimulus control in pigeons. One stimulus consisted of the presentation (once per second) of a 1000-Hz pure tone of 150 msec duration followed by a 2000-Hz pure tone of equal duration; the other was the same except for the reversed order of the frequency components. Results indicated that the frequency pattern and not the loudness pattern of the stimuli was the cue controlling heart-rate changes.     

Sex differences in audiovisual discrimination learning by Bengalese finches (Lonchura striata var. domestica)

Both visual and auditory information are important for songbirds, especially in developmental and sexual contexts. To investigate bimodal cognition in songbirds, the authors conducted audiovisual discrimination training in Bengalese finches. The authors used two types of stimulus: an "artificial stimulus," which is a combination of simple figures and sound, and a "biological stimulus," consisting of video images of singing males along with their songs. The authors found that while both sexes predominantly used visual cues in the discrimination tasks, males tended to be more dependent on auditory information for the biological stimulus. Female responses were always dependent on the visual stimulus for both stimulus types. Only males changed their discrimination strategy according to stimulus type. Although males used both visual and auditory cues for the biological stimulus, they responded to the artificial stimulus depending only on visual information, as the females did. These findings suggest a sex difference in innate auditory sensitivity.     

Stimulus control and compounding with ambient odor as a discriminative stimulus on a free-operant baseline

Previous experiments have demonstrated that the simultaneous presentation of independently established discriminative stimuli can control rates of operant responding substantially higher than the rates occasioned by the individual stimuli. This "additive summation" phenomenon has been shown with a variety of different reinforcers (e.g., food, water, shock avoidance, cocaine, and heroin). Discriminative stimuli previously used in such studies have been limited to the visual and auditory sensory modalities. The present experiment sought to (1) establish stimulus control on a free-operant baseline with an ambient olfactory discriminative stimulus, (2) compare olfactory control to that produced with an auditory discriminative stimulus, and (3) determine whether compounding independently established olfactory and auditory discriminative stimuli produces additive summation. Rats lever pressed for food on a variable-interval schedule in the presence of either a tone or an odor, with comparable control developed to each stimulus. In the absence of these stimuli responding was not reinforced. During stimulus compounding tests, the tone-plus-odor compound occasioned more than double the responses occasioned by either the tone or odor presented individually. Thus, the current study (1) established stimulus control with an ambient olfactory discriminative stimulus in a traditional free-operant setting and (2) extended the generality of stimulus-compounding effects by demonstrating additive summation when olfactory and auditory discriminative stimuli were presented simultaneously.     

Testing a queue hypothesis for the processing of global and local information.

To test whether the advantage for global features in visual perception is stationary throughout the course of processing or is superseded by a local advantage, 6 experiments were conducted in which subjects responded to auditorially presented letter names, while viewing compound visual stimuli. The consistencies of the 2 levels of the compound letters with the auditory stimuli were varied. The requirement with respect to the visual stimulus was manipulated between experiments. The onset asynchrony (SOA) between the visual stimulus and the auditory one was randomized within blocks. Interaction of SOA with consistency of either of the globality levels with the auditory stimulus would indicate lack of stationarity. No such indication was found. Several findings suggest global advantage. The results hold across 3 exposure durations. Findings support the hypothesis of global precedence as well as the claim that it is stationary.     

A multimodal data collection tool using REALbasic and Mac OS X

This project uses REALbasic 3.5 in the Mac OS X environment for development of a configuration tool that builds a data collection procedure for investigating the effectiveness of sonified graphs. The advantage of using REALbasic with the Mac OS X system is that it provides rapid development of stimulus presentation, direct recording of data to files, and control over other procedural issues. The program can be made to run natively on the new Mac OS X system, older Mac OS systems, and Windows (98SE, ME, 2000 PRO). With modification, similar programs could be used to present any number of visual/auditory stimulus combinations, complete with questions for each stimulus.     

Second-order conditioning with diffuse auditory reinforcers in the pigeon

Pigeon subjects were used in five experiments investigating second-order conditioning with visual second-order and diffuse auditory first-order stimuli. Experiment 1 used a discriminative conditioning procedure to demonstrate reliable and substantial second-order conditioning with these stimuli. In Experiments 2 and 3, extinction of the auditory first-order stimulus after second-order conditioning had little effect upon responding to the second-order stimulus, when compared to a stimulus whose reinforcer was maintained. Experiment 4 compared directly the susceptibility of second-order responding to extinction of the first-order reinforcing stimulus as a function of the modality of that reinforcer. When a visual second-order stimulus was paired with a visual reinforcer, and the response to the latter was extinguished, then second-order responding was greatly reduced relative to control levels. In contrast, when that reinforcer was an auditory stimulus, second-order responding was not affected by the current value of the first-order stimulus after conditioning. Finally, in Experiment 5 the auditory stimulus was established as a reinforcer through discriminative-operant training. Following second-order conditioning, extinction of responding to this stimulus again had little impact upon responding to the second-order stimulus with which it had been paired. These results are discussed in terms of previous work on second-order conditioning with rat and pigeon subjects.     

Space aliens and nonwords: stimuli for investigating the learning of novel word-meaning pairs.

We describe a set of pictorial and auditory stimuli that we have developed for use in word learning tasks in which the participant learns pairings of novel auditory sound patterns (names) with pictorial depictions of novel objects (referents). The pictorial referents are drawings of "space aliens," consisting of images that are variants of 144 different aliens. The auditory names are possible nonwords of English; the stimulus set consists of over 2,500 nonword stimuli recorded in a single voice, with controlled onsets, varying from one to seven syllables in length. The pictorial and nonword stimuli can also serve as independent stimulus sets for purposes other than word learning. The full set of these stimuli may be downloaded from www.psychonomic.org/archive/.     

The role of crossmodal competition and dimensional overlap in crossmodal attention switching

Crossmodal selective attention was investigated in a cued task switching paradigm using bimodal visual and auditory stimulation. A cue indicated the imperative modality. Three levels of spatial S–R associations were established following perceptual (location), structural (numerical), and conceptual (verbal) set-level compatibility. In Experiment 1, participants switched attention between the auditory and visual modality either with a spatial-location or spatial-numerical stimulus set. In the spatial-location set, participants performed a localization judgment on left vs. right presented stimuli, whereas the spatial-numerical set required a magnitude judgment about a visually or auditorily presented number word. Single-modality blocks with unimodal stimuli were included as a control condition. In Experiment 2, the spatial-numerical stimulus set was replaced by a spatial-verbal stimulus set using direction words (e.g., “left”). RT data showed modality switch costs, which were asymmetric across modalities in the spatial-numerical and spatial-verbal stimulus set (i.e., larger for auditory than for visual stimuli), and congruency effects, which were asymmetric primarily in the spatial-location stimulus set (i.e., larger for auditory than for visual stimuli). This pattern of effects suggests task-dependent visual dominance.     

A response-spacing effect: an absence of responding during response-feedback stimuli

In most studies of operant reinforcement a response-feedback stimulus is used which is so brief that the nature of the responding during it is virtually undetectable. The present study investigated the nature of this responding by lengthening an initially brief feedback stimulus. The key-pecking responses of pigeons were maintained by a variable-interval schedule of food reinforcement. Each response produced a brief stimulus light in addition to the usual auditory response feedback. When the duration of the feedback stimulus light was gradually increased, it was found to control a nearly zero rate of responding. The result was a paced, metronomic-like performance in which the pigeon made a single response, paused until the stimulus terminated, and then responded again. As a result, the overall response rate was greatly reduced; the mean interresponse time approximated the stimulus duration. A plausible interpretation is that brief feedback stimuli acquire control over responding because they coincide with few responses and few reinforcers. These findings show that in addition to their known functions as conditioned-reinforcing stimuli and discriminative stimuli, response-feedback stimuli also exert direct stimulus control: responding is reduced during the feedback stimulus itself.     

The influence of stimulus properties on multisensory processing in the awake primate superior colliculus.

Multisensory integration is a process whereby information converges from different sensory modalities to produce a response that is different from that elicited by the individual modalities presented alone. A neural basis for multisensory integration has been identified within a variety of brain regions, but the most thoroughly examined model has been that of the superior colliculus (SC). Multisensory processing in the SC of anaesthetized animals has been shown to be dependent on the physical parameters of the individual stimuli presented (e.g., intensity, direction, velocity) as well as their spatial relationship. However, it is unknown whether these stimulus features are important, or evident, in the awake behaving animal. To address this question, we evaluated the influence of physical properties of sensory stimuli (visual intensity, direction, and velocity; auditory intensity and location) on sensory activity and multisensory integration of SC neurons in awake, behaving primates. Monkeys were trained to fixate a central visual fixation point while visual and/or auditory stimuli were presented in the periphery. Visual stimuli were always presented within the contralateral receptive field of the neuron whereas auditory stimuli were presented at either ipsi- or contralateral locations. Many of the SC neurons responsive to these sensory stimuli (n = 66/84; 76%) had stronger responses when the visual and auditory stimuli were combined at contralateral locations than when the auditory stimulus was located on the ipsilateral side. This trend was significant across the population of auditory-responsive neurons. In addition, some SC neurons (n = 31) were presented a battery of tests in which the quality of one stimulus of a pair was systematically manipulated. A small proportion of these neurons (n = 8/31; 26%) showed preferential responses to stimuli with specific physical properties, and these preferences were not significantly altered when multisensory stimulus combinations were presented. These data demonstrate that multisensory processing in the awake behaving primate is influenced by the spatial congruency of the stimuli as well as their individual physical properties.     

Response specificity in animal timing.

The stimuli that control responding in the peak procedure were investigated by training rats, in separate sessions, to make two different responses for food reinforcement. During one type of session, lever pressing was normally reinforced 32 s after the onset of a light. During the other type of session, chain pulling was normally reinforced either 8 s after the onset of one auditory cue or 128 s after the onset of a different auditory cue. For both types of sessions, only the appropriate manipulandum was available, and 20% of the trials lasted 240 s and involved no response-contingent consequences. Rats were then tested with the auditory cues in the presence of the lever and the light in the presence of the chain. If the time of reinforcement associated with each stimulus was learned, response rates should peak at these times during transfer testing. However, if a specific response pattern was learned for each stimulus, little transfer should occur. The results did not clearly support either prediction, leading to the conclusion that both a representation of the time of reinforcement and the rat's own behavior may control responding in this situation.     

Stimulus spacing effects in duration perception are larger for auditory stimuli: Data and a model

Models of duration bisection have focused on the effects of stimulus spacing and stimulus modality. However, interactions between stimulus spacing and stimulus modality have not been examined systematically. Two duration bisection experiments that address this issue are reported. Experiment 1 showed that stimulus spacing influenced the classification of auditory, but not visual, stimuli. Experiment 2 used a wider stimulus range, and showed stimulus spacing effects for both visual and auditory stimuli, although the effects were larger for auditory stimuli. A version of Temporal Range Frequency Theory was applied to the data, and was used to demonstrate that the qualitative pattern of results can be captured with the single assumption that the durations of visual stimuli are less discriminable from one another than are the durations of auditory stimuli.     

Attentional orienting across the sensory modalities

This event-related potential study investigated (i) to what extent incongruence between attention-directing cue and cued target modality affects attentional control processes that bias the system in advance to favor a particular stimulus modality and (ii) to what extent top-down attentional control mechanisms are generalized for the type of information that is to be attended. To this end, both visual and auditory word cues were used to instruct participants to direct attention to a specific visual (color) or auditory (pitch) stimulus feature of a forthcoming multisensory target stimulus. Effects of cue congruency were observed within 200 ms post-cue over frontal scalp regions and related to processes involved in shifting attention from the cue modality to the modality of the task-relevant target feature. Both directing visual attention and directing auditory attention were associated with dorsal posterior positivity, followed by sustained fronto-central negativity. However, this fronto-central negativity appeared to have an earlier onset and was more pronounced when the visual modality was cued. Together the present results suggest that the mechanisms involved in deploying attention are to some extent determined by the modality (visual, auditory) in which attention operates, and in addition, that some of these mechanisms can also be affected by cue congruency.