Compound Stimulus Research Articles

Behavioral and hormonal effects of two weaning situations in trotter foals

Weaning is recognized as being a stressful event for foals. The outcome of this weaning stress can depend upon the procedure that was used. The aim of the present study was to investigate the behavioral and hormonal effects of two different weaning situations in Standardbred trotter foals born in Italy. In situation 1 (10 foals), weaning was performed at around 5 months of age, two foals/week, and foals were handled regularly after weaning in stud 1 (S1). In situation 2 (12 foals) weaning was performed at around 7 months of age, all foals on the same day, and there was little handling after weaning in Stud 2 (S2). Behavioral observations and saliva and hair sampling for RIA cortisol levels assessment were done on day -7, day 0 (weaning day), day 7 and day 30. Behavioral data were analyzed using Generalized Linear Mixed Models, Friedman ANOVAs, U-Mann Whitney tests. Cortisol data were analyzed using repeated measure ANOVAs. Spearman correlations were used to assess correlations. Foals in both studs vocalized (all Bonferroni adjusted P < 0.05) significantly more on the day they had been weaned than on any other day. They also showed a decrease in time spent eating on D0 supporting that weaning was a stressful event for them. The decrease in eating behavior was present also on D7 for S1, but not for S2 foals (S1: Bonferroni adjusted P < 0.05 for contrasts between D0 and D-7/D30; S2: Bonferroni adjusted P < 0.05 for all contrasts between days). Saliva cortisol concentrations differed significantly only depending on “age at the beginning of the experiment” (AB) and sex of the foal, whereas hair cortisol varied depending the day and the interaction day*AB and day*stud (all P < 0.01), with S1 foals having higher hair concentrations than S2 foals on the seventh day after weaning. Results suggest that the weaning situation in stud 1 (which included being weaned two at a time at 5 months of age) could be more stressful for foals than that experienced in stud 2 (which included being weaned all together at 7 months of age). As the weaning situations evaluated in the present experiment were compound stimuli, it would be interesting to confirm them in an experiment in which all features of the compound situation are teased apart (including possible confounding variables, such as stud) and foals are randomly allocated into experimental groups.

Pavlovian occasion setting in human fear and appetitive conditioning: Effects of trait anxiety and trait depression

Contexts and discrete stimuli often hierarchically influence the association between a stimulus and outcome. This phenomenon, called occasion setting, is central to modulation-based Pavlovian learning. We conducted two experiments with humans in fear and appetitive conditioning paradigms, training stimuli in differential conditioning, feature-positive discriminations, and feature-negative discriminations. We also investigated the effects of trait anxiety and trait depression on these forms of learning. Results from both experiments showed that participants were able to successfully learn which stimuli predicted the electric shock and monetary reward outcomes. Additionally, as hypothesized, the stimuli trained as occasion setters had little-to-no effect on simple reinforced or non-reinforced stimuli, suggesting the former were indeed occasion setters. Lastly, in fear conditioning, trait anxiety was associated with increases in fear of occasion setter/conditional stimulus compounds; in appetitive conditioning, trait depression was associated with lower expectations of monetary reward for the trained negative occasion setting compound and transfer of the negative occasion setter to the simple reinforced stimulus. These results suggest that clinically anxious individuals may have enhanced fear of occasion setting compounds, and clinically depressed individuals may expect less reward with compounds involving the negative occasion setter.

Distinguishing signal strength and spatial structure in fMRI pattern analyses of human primary visual cortex

Multivariate pattern analyses are widely used in neuroimaging studies. But it is unclear what these analyses reveal about neural coding. Such approaches often obfuscate the link between neural measurements and the stimulus, greatly limiting their utility. Linear classification, a highly-popular approach, exploits the Euclidean distance among pattern vectors. Our recent theoretical work suggests that information regarding tuning properties is best captured by angular distances, not Euclidean distances. The goal of this experiment was to relate specific aspects of multivariate measurements to parametrically defined dimensions of visual stimuli. We used primary visual cortex as a model system to test the following predictions: (i) Euclidean distances conflate information regarding response amplitude and selectivity, (ii) angular distances best reflect information about selectivity, and (iii) data demeaning—a common preprocessing procedure—invalidates inferences regarding selectivity because it changes angular relationships among pattern vectors. fMRI BOLD activity was measured from 5 participants (7T, 32-channel coil, 1.2x1.2x1.2 mm resolution). Stimuli consisted of Cartesian sinusoidal gratings multiplied by flower-shaped apertures. The orientation of the “petals” was controlled by the phase of the radial frequency (RF) used to generate the aperture. In a fully crossed experimental design, the compound stimulus varied along three dimensions: grating orientation, contrast, and RF-phase, resulting in a total of 96 unique conditions. We found that the Euclidean metric was sensitive to stimulus contrast and relatively insensitive to grating orientation and aperture phase. Angular distances proved sensitive to grating orientation and aperture phase, and robust to changes in stimulus contrast. As predicted, data demeaning led to mischaracterizations of neural tuning. Finally, we used a biologically-inspired image-computable model to provide a theoretic account of these observations. Our results have fundamental implications for the interpretation of MVPA, and inform the development of data analysis strategies that are more readily interpretable in terms of the underlying neurophysiology.

The retrosplenial cortex as a possible “sensory integration” area: A neural network modeling approach of the differential outcomes effect in negative patterning

We explored the hypothesis that learning a Pavlovian negative patterning task would be facilitated when training with differential, as opposed to non-differential, reinforcing outcomes. Two groups of rats received pairings of one visual and one auditory stimulus with food reward when these stimuli were presented on separate training trials, but without reward when both stimuli were presented on simultaneous stimulus compound trials (V+, A+, AV-; similar to an XOR problem). For Group Differential, each stimulus was separately paired with distinctively tasting food rewards, whereas for Group Non-Differential each stimulus was randomly paired with both food reward types across different stimulus element trials. We observed that rats learned the negative patterning task more rapidly and effectively when trained with differential outcomes. These data support a multi-layered connectionist model introduced by Delamater (2012) in which a multi-modal processing structure plays the role of a “sensory integration” area like that hypothesized for the retrosplenial cortex by Dave Bucci and his colleagues (e.g., Todd, Fournier, & Bucci, 2019). We discuss how such a region may develop different “negative occasion setting” and “configural inhibition” mechanisms in solving negative patterning and related tasks.

The effectiveness of visual and auditory elements of a compound stimulus in controlling behavior in the domestic dog (Canis familiaris)

This study measured the responses of dogs to signals delivered via hand and voice signals. The study sought to determine whether dogs would display differential stimulus control when switching from a compound stimulus (auditory-visual) cue to presentation of only one of its elements. Twelve dogs performed a target behavior in response to a 2-element compound stimulus composed of a hand (visual modality) signal and a voice (auditory modality) signal. The mean percent correct responses to the visual element (M = 56.5, SD = 20.74) and the auditory element (M = 67.5, SD = 21.57) were both significantly lower than the 85% correct for the compound stimulus, P < 0.017. There was also evidence of a preference for one of the elements of the compound stimulus. The mean percent correct for the more favoured element (M = 77.25, SD = 12.53) was significantly higher than for the less favoured element (M = 46.75, SD = 17.2), P < 0.001. The identity of the favoured element was not consistent across the animals with 75% preferring the auditory element and 25% the visual element. This study contributes to an understanding of factors related to the stimulus control of learned behaviors. The differential control of behavior by alternative cues has implications for the training of assistance or service and other working animals with multiple cues. The results would strongly suggest that training with a compound stimulus is not appropriate if only elements of the compound stimulus are to be subsequently used.

Relationship between reinforcement rate and response rate in Pavlovian and operant conditioning with compound stimuli in rats

Harris, Andrew, and Livesey (2012) proposed that response rate (R) to a stimulus (e.g., A) of a compound (e.g., AB) would be directly related to the difference between reinforcement rate (r) during AB and the other stimulus (e.g., B). To explore the extent of this proposal to operant conditioning, three experiments were carried out. Experiment 1 replicated Harris et al. (2012 – Experiment 1) using sucrose as US in Pavlovian conditioning. In Experiment 2 rats pressed a lever under a variable interval schedule in two phases. In Training, responses during a compound stimulus AB100% were reinforced 100%, responses during B50% and C50% 50% and responses during D25%, 25% of the trials. Then, nonreinforced A trials were introduced (Probe). Results from Experiment 2 showed that r controlled the R to AB100%, B50%, C50% and D25% during training and probe, however, were inconclusive about r and R relationship during A. In Experiment 3, responses during A100% were reinforced 100% and during B50% and C50% 50% of the trials (Training). Next, nonreinforced BC trials were presented (Probe). Results from Experiment 3 showed that response rate during BC were similar to A100%, but higher than B50% and C50%, suggesting summation of B50% and C50% reinforcement rates. Overall, the results showed that Harris et al. (2012) proposal extends to discriminative operant relations.

Learning simple and compound stimuli in a social lizard (Egernia stokesii).

We tested learning and behavioral flexibility in family-living gidgee skinks (Egernia stokesii) using a multistage visual discrimination task that included acquisition and reversal stages using simple and compound stimuli composed of black shapes superimposed on a colored background. We evaluated how lizards learn compound cues through a probe test. Lizards showed behavioral flexibility through reversal learning using simple stimuli (only color or shape). Our lizards used compound stimuli to learn a discrimination but had problems reversing and generalizing across novel compound stimuli. In the probe test, lizards chose the correct stimulus in a novel pairing with a distractor feature even without previous experience with compound stimuli. Our results suggest that some lizards are likely able to attend selectively to the relevant features of our compound stimuli while ignoring irrelevant features instead of using the configuration of a cue card as a whole to learn to discriminate between compound stimuli. We hope that our work will spark interest in further studies looking at how lizards (and reptiles in general) learn to solve visual discrimination problems. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Exploring effects of differential observing responses on vocal tact acquisition

AbstractTwo studies were conducted to explore the effects of differential observing responses (DORs) on vocal tact acquisition in preschool‐age children of typical development. In Study 1 with three participants, an identity‐matching DOR was incorporated into tact instruction trials with novel visual stimuli. Acquisition rates were similar in the DOR condition and in a non‐DOR condition. In Study 2 with five new participants, the identity‐matching DOR was implemented as an intervention when standard discrete‐trial instruction failed to produce acquisition of tacts of compound stimuli. Two participants reached mastery after the identity‐matching DOR was introduced, whereas three participants' progress was unaffected. For those three, the identity‐matching DOR was replaced with a verbal DOR (tacting of stimulus components), but although one participant's correct responding increased, none reached mastery. Two participants ultimately reached mastery after a non‐DOR intervention. Conditions under which DORs facilitate stimulus control outside of MTS tasks remain to be identified.

Learning Channels: The Role of Compound Stimuli in the Emergence of Intraverbal Relations in Children on the Autism Spectrum.

Teaching tact and intraverbal responses based on function-feature-class to children with language delays can result in the emergence of untrained relational responses. The purpose of this study was to compare the effects of compound stimuli in discriminated operants (i.e., different combinations of hear, see, touch, and taste) on the acquisition of object-attribute relations, on the emergence of untrained attribute-object relations, and on the acquisition and emergence of same-different relations between objects and their attributes. All the participants were on the autism spectrum and between 4 and 12 years old. Participants who did not meet the mastery criterion or show emergent intraverbal responses during initial training trials completed a fluency-based practice phase. Overall results showed that all six participants required fewer trials to meet the criterion in the condition involving compound stimuli (e.g., HearSeeSay plus Touch, Taste, or Sniff) as compared to the HearSeeSay-alone condition. In addition, participants required fewer fluency practice timings in the condition involving compound stimulito meet fluencyaim.

Blocking of Stimulus Control in Children with Autism

The present study aimed to investigate the blocking of stimulus control in three children with autism. We used a go/no-go procedure in a standard blocking paradigm. In Phase 1, we established one of two sounds or colored squares as a discriminative stimulus for touching a tablet screen. In Phase 2, a colored square was added to the sound or a sound was added to the colored square in a stimulus compound. The discrimination training continued as in Phase 1. We subsequently tested discriminative control by each of the single stimuli separately and by the compounds. Finally, after testing with no programmed consequences, we reestablished the original discrimination and replicated the test of stimulus control. The results support previous experiments by demonstrating that the establishment of discriminative control by a second stimulus by adding it to a previously established discriminative stimulus in a compound was blocked by the earlier discrimination training in all three participants. We discuss procedural details that may be critical to avoid the blocking of stimulus control in the applied field, particularly with respect to the acquisition of skills that involve multiple stimuli, such as joint attention, social referencing, and bidirectional naming.

Supplemental Material for Learning Simple and Compound Stimuli in a Social Lizard (Egernia stokesii)

Supplemental Material for Learning Simple and Compound Stimuli in a Social Lizard (Egernia stokesii)

Mechanisms of perceptual learning: Prolonged intermixed preexposure reduces the effectiveness of the unique and the common elements.

In three experiments, rats were given intermixed or blocked preexposure to two similar compound stimuli, AX and BX. In Experiment 1, following preexposure, animals were given appetitive conditioning training with the compound AX. A subsequent generalization test showed better discrimination between AX and BX in the group given intermixed than in the one given blocked preexposure. Experiments 2 and 3 assessed the nature of the learning mechanisms underlying this instance of the perceptual learning effect. Experiment 2 assessed the associability of the common and unique elements (X and A); animals in the group given intermixed preexposure showed poorer conditioning with both the X and the A elements than those given blocked preexposure. Experiment 3 further assessed the perceptual effectiveness of the distinctive element A using a superimposition test (the capacity of A to interfere with the conditioned response commanded by an independent conditioned stimulus). The results showed, in line with the outcome of Experiment 2, that the unique element A is more salient following blocked than intermixed preexposure. These results are discussed by reference to current theories of perceptual learning. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Auditory–Visual stimuli: Effects on derived relations with compound stimuli

AbstractThis research explored the effect of teaching conditional discriminations with three procedures on the derivation of 36 stimuli relations (derived relations). The stimuli used consisted of three characteristics musical instruments, along with the corresponding picture. In the first experiment six university students were trained with simple stimuli and tested with compound auditory–visual samples; therefore, a one‐to‐many structure was used. In the second experiment, auditory stimuli were replaced by visual stimuli, for the samples used, for new students. A third experiment was implemented with an extra phase of training with compound stimuli for six new students. The structure of the experiments was: pretests (Xbcd–A; Xacd–B; Xabd–C; Xabc–D), training (A–B; A–C; A–D), and posttests (same as pretests). The difference between these conditions was the kind of stimuli used and a new phase of teaching used in condition 3: (Xbcd–A). The results indicate that training with simple stimuli on discriminations that include stimuli that are easy to discriminate from each other (words and sounds) is a sufficient condition for good posttest performance. However, when comparisons are made difficult (words only), participants show better performance on new tests if they have a learning history with compound stimuli.

Numerical averaging in mice.

Rodents can be trained to associate different durations with different stimuli (e.g., light/sound). When the associated stimuli are presented together, maximal responding is observed around the average of individual durations (akin to averaging). The current study investigated whether mice can also average independently trained numerosities. Mice were initially trained to make 10 or 20 lever presses on a single (run) lever to obtain a reward and each fixed-ratio schedule was signaled either with an auditory or visual stimulus. Then, mice were trained to press another lever to obtain the reward after they responded on the run lever for the minimum number of presses [Fixed Consecutive Number (FCN)-10 or -20 trials] signaled by the corresponding discriminative stimulus. Following this training, FCN trials with the compound stimulus were introduced to test the counting behavior of mice when they encountered conflicting information regarding the number of responses required to obtain the reward. Our results showed that the numbers of responses on these compound test trials were around the average of the number of responses in FCN-10 and FCN-20 trials particularly when the auditory stimulus was associated with a fewer number of required responses. The counting strategy explained the behavior of the majority of the mice in the FCN-Compound test trials (as opposed to the timing strategy). The number of responses in FCN-Compound trials was accounted for equally well by the arithmetic, geometric, and Bayesian averages of the number of responses observed in FCN-10 and FCN-20 trials.

Still the same in human causal reasoning: Evidence for a uniform similarity parameter in generalisation and summation.

Wagner's replaced elements model (REM) theory implies that generalisation and summation tests depend on a common similarity parameter, but few studies have assessed generalisation and summation within the same experimental paradigm. Three experiments adapted a methodology used in non-human animal studies to investigate this question in the case of human causal reasoning. The studies combined different amounts of training on simple discriminations (A+ vs. C-), compound discriminations (AB+ vs. CD-), and irrelevant novel cue discriminations (An+ vs. Cn-) with testing on single cues, compound cues, and compounds of cues with novel cues. The results were compared with predictions of Pearce's configural model and Wagner's REM elemental model. They also were examined to determine whether generalisation and summation could be accounted for using a single value for the similarity between stimulus compounds and the separable constituent cues of which the compounds were composed. The findings indicated that each theory needed to include common cues to account for the data.

Biased Neural Representation of Feature-Based Attention in the Human Frontoparietal Network.

Selective attention is a core cognitive function for efficient processing of information. Although it is well known that attention can modulate neural responses in many brain areas, the computational principles underlying attentional modulation remain unclear. Contrary to the prevailing view of a high-dimensional, distributed neural representation, here we show a surprisingly simple, biased neural representation for feature-based attention in a large dataset including five human fMRI studies. We found that when human participants (both sexes) selected one feature from a compound stimulus, voxels in many cortical areas responded consistently higher to one attended feature over the other. This univariate bias was consistent across brain areas within individual subjects. Importantly, this univariate bias showed a progressively stronger magnitude along the cortical hierarchy. In frontoparietal areas, the bias was strongest and contributed largely to pattern-based decoding, whereas early visual areas lacked such a bias. These findings suggest a gradual transition from a more analog to a more abstract representation of attentional priority along the cortical hierarchy. Biased neural responses in high-level areas likely reflect a low-dimensional neural code that can facilitate a robust representation and simple readout of cognitive variables.SIGNIFICANCE STATEMENT It is typically assumed that cognitive variables are represented by distributed population activities. Although this view is rooted in decades of work in the sensory system, it has not been rigorously tested at different levels of cortical hierarchy. Here we show a novel, low-dimensional coding scheme that dominated the representation of feature-based attention in frontoparietal areas. The simplicity of such a biased code may confer a robust representation of cognitive variables, such as attentional selection, working memory, and decision-making.

Reading comprehension with the Go/No-Go procedure with compound stimuli.

The present study investigated whether the Go/No-Go procedure with compound stimuli produces emergent relations among dictated words (A), pictures (B), and printed words (C) and the emergence of textual behavior (CD) using a multiple probe design across word sets. Three preschool children were exposed to 4 phases: (1) pretests for BC, CB, and CD relations, (2) pretraining with known stimuli, (3) AB and AC training, and (4) posttests for BC, CB, and CD relations. During AB and AC training, responses to A1B1, A2B2, A1C1, and A2C2 compound stimuli, but not to A1B2, A2B1, A1C2, and A2C1, were reinforced. The results showed that all participants met the learning criterion and demonstrated emergence of BC and CB relations (i.e., relations between pictures and printed words), and CD relations (i.e., textual behavior) after training. These results suggest that the Go/No-Go procedure with compound stimuli is an effective alternative for establishing reading comprehension.

The representation of stimulus conjunction in theories of associative learning: A context-dependent added-elements model.

This article briefly reviews 3 theories concerning elemental and configural approaches to stimulus representation in associative learning and presents a new context-dependent added-elements model (C-AEM). This model takes an elemental approach to stimulus representation where individual stimuli are represented by single units and stimulus compounds activate both those units and configurational units corresponding to each conjunction of 2 or more stimuli. Activity across these units is scaled such that each stimulus always contributes the same amount of activity to the system whether it is presented in isolation or in compound; the configurational units "borrow" activity from representational units for individual stimuli (and from each other). This scaling is affected by the extent to which stimuli interact with each other perceptually. Hence, the model is conceptually similar to Wagner's (2003) replaced elements model but lacks features that explicitly code for the absence of stimuli (i.e., inhibited elements). Simulations of the model are reported for a range of generalization and discrimination learning tasks, conflicting results from which have previously been taken to provide support for either configural or elemental theories of learning. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Influence of Verbal Behavior Training on Performance for Sustainable Development in Childhood and Early Adolescence

The effective teaching of language is an aspect of special relevance regarding the good adjustment of children in contexts such as school, family, or community. This article performs an experimental procedure to check which language teaching methodology is most effective in a sample of children. The objective was to analyze the influence of training, Condition 1 (pure tacts more intraverbal) or Condition 2 (pure tacts more impure tacts), on emergence of two tests involving impure tacts (AB-C, AB-D) and four new complex intraverbals (BC-D, BD-C) for each of two sets of stimuli (Set 1 and Set 2). The sample comprised 54 children aged between 6 and 12 years, divided into two groups of different experimental conditions. The results revealed statistically significant differences in performance on the tests of impure tacts and complex intraverbal, obtaining highly effective results in Condition 2. This teaching method using compound stimuli (impure tacts) clearly favors the expansion of language. The practical implications of this work can be more effective language teaching methodologies implemented that favor the good psychosocial adjustment of children in contexts such as family, school, or the community in general.

Memory reconsolidation impairments in sign-tracking to an audiovisual compound stimulus

Studies of memory reconsolidation of pavlovian memories have typically employed unimodal conditioned stimuli, despite the use of multimodal compound stimuli in other settings. Here we studied sign-tracking behaviour to a compound audiovisual stimulus. First, we observed not unexpectedly that sign-tracking was poorer to the audiovisual compound than to unimodal visual stimuli. Then, we showed that, depending on the parameters of compound stimulus re-exposure at memory reactivation, systemic MK-801 treatment either impaired extinction to improve sign-tracking at test, or disrupted reconsolidation to impair test behaviour. When memory reactivation consisted of re-exposure to only the auditory component of the compound stimulus, we observed sign-tracking impairments following MK-801 treatment, but only under certain test conditions. This was in contrast to the consistent impairment following reactivation with the full audiovisual compound. Moreover, the parameters of auditory stimulus presentation to enable MK-801-induced impairment at test varied depending on whether the stimulus was presented within or outside the training context. These findings suggest that behaviour under the control of appetitive pavlovian compound stimuli can be modulated by targeting both extinction and reconsolidation, and that it is not necessary to re-expose to the full compound stimulus in order to achieve a degree of modulation of behaviour.