Emergent conditional discrimination in children: Matching to compound stimuli

This study reports two experiments that first taught preschool children identity-matching to compound sample and compound comparison stimuli. A compound stimulus consisted of a colour and a form superimposed on one another. Test sessions assessed whether children related the form and colour elements of a particular compound stimulus. The test for this was matching to sample in which an arbitrary conditional discrimination was required. A majority of the children selected the correct colour comparison in the presence of each form sample. The children also showed the reverse sample-comparison relations: they matched form comparisons to the corresponding colour samples, respectively. In the context of these arbitrary relations, new colours were paired with the form elements of the samples (Experiment 1), and new form elements were paired with the colour elements of the comparisons (Experiment 2). Subsequent tests assessed whether the new stimulus elements had control over responding when presented as single samples or comparisons. Test results showed that most subjects were able to relate the new stimulus elements to the corresponding colour and form elements, respectively. The study demonstrated that matching to compound stimuli in training and testing conditionsMaygenerate conditional relations between the individual stimulus elements.     

Emergent simple discrimination in children: Transfer of stimulus control under non-reinforced conditions

Previous research on humans suggests that simple discriminations may emerge if both stimuli, B1 and B2, are compounded with the stimuli of a previously trained discrimination, A1 (S+) and A2 (S-), and responding to the compounds, B1A1 and B2A2, is reinforced. Two questions were addressed. First, do simple discriminations also emerge if (a) only one stimulus, B1, is compounded with a training stimulus, A1 (S+) or A2 (S-); or with both training stimuli, A1 (S+) and A2 (S-); and (b) neither B1 nor B2 is compounded with the training stimuli? Second, do simple discriminations emerge if reinforcement in the presence of the AB compounds is withheld? Normal preschool children served as subjects. The study consisted of six experiments. Transfer occurred in all experiments regardless of whether both test stimuli, one test stimulus, or none of the test stimuli were compounded with the training stimuli under non-reinforced conditions. The results can be described by the following rules: Respond to any stimulus that includes a component of a “correct” stimulus of a previous discrimination. Otherwise, respond away from the stimulus that incorporates a component from an “incorrect” stimulus of a previous discrimination. The implications of data for sensory pre-conditioning and language-based accounts are discussed.     

Emergent simple discrimination established by indirect relation to differential consequences

Three experiments examined a discrimination training sequence that led to emergent simple discrimination in human subjects. The experiments differed primarily in their subject populations. Normally capable adults served in the first experiment, preschool children in the second, and mentally retarded adults in the third. In all experiments, subjects learned a simple simultaneous discrimination: When visual stimuli A1 and A2 were displayed together, reinforcers followed selections of A1, the S+, but not A2, the S-. The subjects also learned a conditional discrimination taught with an arbitrary visual-visual matching-to-sample procedure. Comparisons were two additional visual stimuli, B1 and B2, and samples were A1 and A2. Reinforcers followed selections of B1 in the presence of A1 and of B2 in the presence of A2. After the simple-discrimination and conditional-discrimination baselines had been acquired, B1 and B2 were displayed alone (without a sample) on probe trials. Subjects had never been taught explicitly how to respond to such displays. Nonetheless, they almost always selected B1, which was involved in a conditional relation with A1, the stimulus that served as S+ on the simple-discrimination trials. This outcome suggested the formation of stimulus classes during conditional-discrimination training. Through class formation, B1 and B2 had apparently acquired stimulus functions similar to those shown by A1 and A2 on simple-discrimination trials, thereby leading to emergent selections of B1 on the probes.     

An analysis of emergent simple discrimination in children

In Experiment 1 eight five-year-old children received an arbitrary matching-to-sample task with sample stimuli A1 and A2 and comparison stimuli B1 and B2. This task was mixed with a simple, two-choice discrimination task with stimuli A1 and A2. In subsequent tests with B1 and B2 presented alone, the number of responses to B1 was greater when it had been paired with the correct stimulus of the simple discrimination task than when it had been paired with the incorrect stimulus. In Experiment 2 incorrect comparisons were omitted during the matching-to-sample task. Eight children were taught to point to either A1 or A2 first, and to either B1 or B2 second. Eight other children were taught to point to either B1 or B2 first, and to either A1 or A2 second. The effect of Experiment 1 was replicated with the first but not with the second group. The results of both experiments suggest that the functions of S+ and S- in a simple discrimination task can transfer to test stimuli if the training stimuli precede the test stimuli during paired presentations.     

Unfamiliar voice discrimination for short stimuli in newborns

In order to determine the minimal information required for newborns to discriminate unfamiliar voices two experiments were performed using the presentation of single disyllabic words uttered by male and female speakers. In the first experiment, utilizing the standard high‐amplitude‐sucking procedure, no significant discrimination was obtained. Hypothesizing that this failure in discrimination could be due to a deficient attention at the unique moment of stimulus change, a second experiment was performed in which the same to‐be‐discriminated stimuli alternated every minute and in which multiple tokens of the same word were presented to increase stimulus variability. Evidence for voice discrimination was obtained, suggesting that newborns are able to characterize unfamiliar voices on the basis of restrained vocal‐tract related information and minor prosodic information. Remarks addressing the consequences of stimulus organization upon attentional demands in experimental procedures in young infants are also presented.     

Minimally-effective interpolated stimuli in weight discrimination

The question of minimally effective weights was investigated by using an interpolated anchor paradigm. The weight series of 100 to 300 g,at 50-g-step intervals, was shown to be significantly affected by an interpolated anchor of 0.5 g, thus demonstrating a reduction in the region of ineffectiveness. The results were discussed in terms of procedural artifacts in the weight-judging methods reported in previous literature.     

Attending to the non-preferred hand improves bimanual coordination in children

The effect of attentional focus in bimanual coordination was investigated from a developmental perspective by examining performance of right- and left-handed children, 5-8-years and 9-12-years old, on bimanual reciprocal tapping tasks. Attentional focus was either specified, by asking the children to attend to the preferred or to the non-preferred hand, or unspecified for the execution of the tasks. When attention was oriented to the non-preferred hand we found a reduced movement time and a lower frequency of errors. Performance differences for handedness and age-groups were observed when the children were oriented to attend to the preferred hand or when there was no instruction regarding attention. These differences in performance were eliminated when attention was oriented to the non-preferred hand.     

Preference for and discrimination of videos of conspecific social behavior in mice

We showed mice videos of three conspecific social behaviors, namely sniffing, copulation, and fighting, in pairwise combinations using iPods and evaluated preference as determined by time spent in front of each iPod. Mice preferred the copulation video to the sniffing video, the fighting video to the sniffing video, and the fighting video to the copulation video. In Experiment 1a, we used a single video clip for each social behavior but used multiple video clips for each social behavior in Experiment 2a. Next, we trained mice to discriminate between the fighting and copulation videos using a conditioned-place-preference-like task in which one video was associated with injection of morphine and the other was not. For half of the subjects, the fighting video was associated with morphine injection, and for the other half, the copulation video was associated with morphine injection. After conditioning, the mice stayed longer in the compartment with the morphine-associated video. When tested with still images obtained from the videos, mice stayed longer in the compartment with still images from the video associated with morphine injection (Experiment 1b). When we trained mice with multiple exemplars, the subjects showed generalization of preference for new video clips never shown during conditioning (Experiment 2b). These results demonstrate that mice had a preference among videos of particular behavior patterns and that they could discriminate these videos as visual category. Although relationship between real social behaviors and their videos is still open question, the preference tests suggest that the mice perceived the videos as meaningful stimuli.     

Conditional discrimination and equivalence relations: Control by negative stimuli

Three adult subjects were taught the following two-sample, two-comparison conditional discriminations (each sample is shown with its positive and negative comparison, in that order): A1-B1B2, A2-B2B1; B1-C1C2, B2-C2C1; and C1-D1D2, C2-D2D1. A teaching procedure was designed to encourage control by negative comparisons. Subjects were then tested for emergent performances that would indicate whether the baseline conditional discriminations were reflexive, symmetric, and transitive. The tests documented the emergence of two classes of equivalent stimuli: A1, B2, C1, D2 and A2, B1, C2, D1. These were the classes to be expected if the negative comparisons were the controlling comparisons in the baseline conditional discriminations. The negative comparisons, however, were not the comparisons that subjects were recorded as having chosen in the baseline conditional discriminations. Differential test results confirmed predictions arising from a stimulus-control analysis: In reflexivity tests (AA, BB, CC, DD), subjects chose comparisons that differed from the sample; one-node transitivity (AC, BD) and "equivalence" (CA, DB) tests also yielded results that were the opposite of those to be expected from control by positive comparisons; symmetry tests (BA, CB, DC), two-node transitivity (AD) tests, and two-node "equivalence" (DA) tests yielded results that were to be expected from control by either positive or negative comparisons.     

Nonword repetition stimuli for Vietnamese-speaking children

Nonword repetition (NWR) has been a widely used measure of language-learning ability in children with and without language disorders. Although NWR tasks have been created for a variety of languages, minimal attention has been given to Asian tonal languages. This study introduces a new set of NWR stimuli for Vietnamese. The stimuli include 20 items ranging in length from one to four syllables. The items consist of dialect-neutral phonemes in consonant–vowel (CV) and CVC sequences that follow the phonotactic constraints of the language. They were rated high on wordlikeness and have comparable position segments and biphone probabilities across stimulus lengths. We validated the stimuli with a sample of 59 typically developing Vietnamese–English bilingual children, ages 5 to 8. The stimuli exhibited the expected age and length effects commonly found in NWR tasks: Older children performed better on the task than younger children, and longer items were more difficult to repeat than shorter items. We also compared different scoring systems in order to examine the individual phoneme types (consonants, vowels, and tones) and composite scores (proportions of phonemes correct, with and without tone). The study demonstrates careful construction and validation of the stimuli, and future directions are discussed.     

The two-alternative observing response procedure in rats: Preference for nondiscriminative stimuli and the effect of delay

A two-alternative choice procedure was used with rats to examine preference for discriminative stimuli (correlated with the occurrence of reinforcement) versus uncorrelated cues. Choice of discriminative stimuli was below chance, despite the use of very low levels of reinforcement (12.5% for some rats) known to produce a preference for discriminative cues. Levers that had been retracted during the stimulus presentation in Experiment 1 were extended in Experiment 2 to assess the role of response elicitation during the observed stimuli. In Experiment 3, the impact of cue-duration behaviors was further evaluated by lengthening the duration of the cues and providing an opportunity for an escape response. The preference for nondiscriminative stimuli was reversed only with increased exposure to the cues. The present results point to fundamental differences in the prevailing context of the choice procedure as compared to the usual free-operant observing design.     

Visual working memory for simple and complex visual stimuli

Does the magical number four characterize our visual working memory (VWM) capacity for all kinds of objects, or is the capacity of VWM inversely related to the perceptual complexity of those objects? To find out how perceptual complexity affects VWM, we used a change detection task to measure VWM capacity for six types of stimuli of different complexity: colors, letters, polygons, squiggles, cubes, and faces. We found that the estimated capacity decreased for more complex stimuli, suggesting that perceptual complexity was an important factor in determining VWM capacity. However, the considerable correlation between perceptual complexity and VWM capacity declined significantly if subjects were allowed to view the sample memory display longer. We conclude that when encoding limitations are minimized, perceptual complexity affects, but does not determine, VWM capacity.     

Transfer across unconditioned stimuli in serial feature discrimination training

The transfer of conditioned modulation across conditioned stimuli (CS) and unconditioned stimuli (US) was examined in 3 experiments that used Pavlovian appetitive training procedures with rats. In Experiment 1, after training in a positive patterning discrimination (X-->A+/X-/A-), X increased conditioned responding elicited by another trained-then-extinguished CS as long as that CS had been trained with the same US as was used in discrimination training. In Experiment 2, after training with a feature-negative discrimination (X-->A-/A+), X inhibited conditioned responding elicited by another trained-then-extinguished CS as long as that CS had been trained with the same US. Experiments 1 and 2 used a between-groups design, whereas Experiment 3 used a more powerful within-groups design. In Experiment 3, rats were trained in a feature-positive discrimination (X-->A+/A-). In transfer tests, X increased conditioned responding elicited by another CS trained then extinguished with the same US from training. This increase was greater than the X increased conditioned responding elicited by another CS trained then extinguished with a different US from training. The results supported the suggestion that features trained in serial discrimination tasks influence behavior indirectly by transiently raising or lowering the threshold for activation of the US representations by its target stimuli and by any other stimuli that may be associated with that US. Other interpretations of the findings were also considered.