AN ANALYSIS OF MAINTENANCE FOLLOWING FUNCTIONAL COMMUNICATION TRAINING

The multiple and long-term effects of functional communication training relative to a common reductive procedure (time-out from positive reinforcement) were evaluated. Twelve children participated in a functional analysis of their challenging behaviors (Study 1), which implicated adult attention as a maintaining variable. The children were then matched for chronological age, mental age, and language age and assigned to two groups. One group received functional communication training as an intervention for their challenging behavior, and the second group received time-out as a contrast. Both interventions were initially successful (Study 2), but durable results were achieved only with the group that received functional communication training across different stimulus conditions (Study 3). Students whose challenging behaviors were previously reduced with time-out resumed these behaviors in the presence of naive teachers unaware of the children's intervention history. The value of teaching communicative responses to promote maintenance is discussed as it relates to the concept of functional equivalence.     

Infants' responsiveness to the auditory and visual attributes of a sounding/moving stimulus.

Responses to unimodal and multimodal attributes of a compound auditory/visual stimulus were investigated in 4-, 6-, 8-, and 10-month-old infants. First, infants were habituated to a compound stimulus consisting of a visual stimulus that moved up and down on a video monitor and a sound that occurred each time the visual stimulus reversed direction at the bottom. Once each infant met a habituation criterion, a series of test trials was administered to assess responsiveness to the components of the compound stimulus. Response was defined as the total duration of visual fixation in each trial. In the two unimodal test trials, the rate at which the component was presented was changed while the rate of the other component remained the same, whereas in the bimodal test trial the rate of both components was changed simultaneously. Results indicated that infants at each age successfully discriminated the bimodal and the two unimodal changes and that regression to the mean did not account for the results. Results also showed that disruption of the temporal relationship that accompanied the change in rate in the two unimodal test trials was also discriminable, but rate changes appeared to play a greater role in responsiveness than did synchrony changes. Considered together with results from similar prior studies, the current results are consistent with the modality appropriateness hypothesis in showing that discrimination of temporal changes in the auditory and visual modalities is dependent on the specialization of the sensory modalities.     

On the relation between auditory spatial attention and auditory perceptual asymmetries.

Laterality investigators have typically interpreted any perceptual asymmetry as a direct expression of the functional organization of the brain. However, many other confounding factors, including the asymmetric distribution of attention, may also contribute to either the magnitude or the direction of any of these advantages. In two experiments, attention was manipulated in a dichotic listening paradigm by presenting a preexposural tone cue to the ear from which the subject was required to report. The time available to orient attention was manipulated by varying the time period between the onset of the cue and the onset of the trial (stimulus onset asynchrony, or SOA). Results indicated that a right ear advantage for the identification of verbal material obtained at a 150-msec SOA was almost completely eliminated at an SOA of 450 msec. In addition, the direction of the ear advantage for emotion identification was found to depend on task difficulty. A left ear advantage, apparent when task difficulty was minimal, was reversed to a right ear advantage when difficulty was increased. These data are taken as evidence that, when subjects are faced with a difficult dichotic task, there is a general tendency for right-handed subjects to bias their attention toward the right ear. Such a tendency is shown not only to have likely seriously compromised the results of past investigations of functional perceptual asymmetries but also to be inconsistent with previously proposed theories of dichotic listening performance.     

Surface perception in pictures.

Subjects adjusted a local gauge figure such as to perceptually "fit" the apparent surfaces of objects depicted in photographs. We obtained a few hundred data points per session, covering the picture according to a uniform lattice. Settings were repeated 3 times for each of 3 subjects. Almost all of the variability resided in the slant; the relative spread in the slant was about 25% (Weber fraction). The tilt was reproduced with a typical spread of about 10 degrees. The rank correlation of the slant settings of different observers was high, thus the slant settings of different subjects were monotonically related. The variability could be predicted from the scatter in repeated settings by the individual observers. Although repeated settings by a single observer agreed within 5%, observers did not agree on the value of the slant, even on the average. Scaling factors of a doubling in the depth dimension were encountered between different subjects. The data conformed quite well to some hypothetical fiducial global surface, the orientation of which was "probed" by the subject's local settings. The variability was completely accounted for by single-observer scatter. These conclusions are based upon an analysis of the internal structure of the local settings. We did not address the problem of veridicality, that is, conformity to some "real object."     

Spatial attention in Ponzo-like patterns.

A variant of Ponzo's pattern was devised by drawing converging oblique lines at the ends of each of two horizontal lines that were located directly one above the other. Pairs of converging or diverging fins (either between or outside the horizontal shafts) were systematically removed. The results showed that, as predicted by integrative field theory, oblique lines between the shafts produced more distortion than did oblique lines outside the shafts. Also, it was shown that the attentive field construct in integrative field theory was crucial for predicting patterns of means and variances in this experiment. The modified Ponzo effect was shown to have much in common with the classical Müller-Lyer illusion. The subtle differences between the two were explained by proposing that the size of the optimum attentive field was larger in the Ponzo tasks than in the Müller-Lyer tasks because expansion fins are found on both shafts in the Ponzo-like figure.     

Adaptation to auditory motion in the horizontal plane: effect of prior exposure to motion on motion detectability.

Thresholds for auditory motion detectability were measured in a darkened anechoic chamber while subjects were adapted to horizontally moving sound sources of various velocities. All stimuli were 500-Hz lowpass noises presented at a level of 55 dBA. The threshold measure employed was the minimum audible movement angle (MAMA)--that is, the minimum angle a horizontally moving sound must traverse to be just discriminable from a stationary sound. In an adaptive, two-interval forced-choice procedure, trials occurred every 2-5 sec (Experiment 1) or every 10-12 sec (Experiment 2). Intertrial time was "filled" with exposure to the adaptor--a stimulus that repeatedly traversed the subject's front hemifield at ear level (distance: 1.7 m) at a constant velocity (-150 degrees/sec to +150 degrees/sec) during a run. Average MAMAs in the control condition, in which the adaptor was stationary (0 degrees/sec,) were 2.4 degrees (Experiment 1) and 3.0 degrees (Experiment 2). Three out of 4 subjects in each experiment showed significantly elevated MAMAs (by up to 60%), with some adaptors relative to the control condition. However, there were large intersubject differences in the shape of the MAMA versus adaptor velocity functions. This loss of sensitivity to motion that most subjects show after exposure to moving signals is probably one component underlying the auditory motion aftereffect (Grantham, 1989), in which judgments of the direction of moving sounds are biased in the direction opposite to that of a previously presented adaptor.     

The effects of complexity on the perception of vibrotactile patterns presented to separate fingers.

Pairs of vibrotactile patterns were presented to subjects' left middle and index fingerpads (unilateral presentation) or left and right index fingerpads (bilateral presentation), using two Optacon arrays. A set of simple (one-line) patterns and a set of complex (two-line) patterns were constructed so that they were equally identifiable when presented individually. In Experiment 1, discrimination performance was lower for two-line patterns than it was for one-line patterns, and it was lower for unilateral presentation than it was for bilateral presentation. Communality, the number of lines that two patterns share in common, was a major factor in reducing discrimination performance for two-line patterns. Subjects' abilities to identify one member of the pair of patterns were measured in Experiment 2. There were no significant differences in performance between pattern sets or type of presentation when subjects attended to a single pattern. However, when subjects were required to attend to both patterns, identification performance was lower for two-line patterns than it was for one-line patterns, and it was lower for unilateral presentation than it was for bilateral presentation. The results suggest that there are limited attentional resources for processing vibrotactile patterns and that more resources are available bilaterally than are available unilaterally.     

Preference can be more powerful than detection of oddity as a test of discriminability.

Subjects presented with sets of three samples, two of distilled water and one of tap water, were significantly more consistent in choosing the tap water as preferable than they were in identifying it as the odd sample in the set. The result is opposite to the prediction of high-threshold models of sensory discrimination, which say that if a difference is not noticed, preferences will be random, whereas if a difference is noticed, preferences may still be in either direction. The result can be quantitatively explained by a model advanced by Frijters to explain an analogous anomaly found with the triangle test used in the food industry. Applying his model to the observed proportions yields essentially equivalent estimates of sensory difference (d' = 1.5, approximately) from the two tasks, and a direction of preference almost unanimously in favor of the tap water that was used. Since the model predicts that the proportion of subjects choosing the odd item will depart further from chance in the preference task than in the oddity task, the former has greater power to reject the null hypothesis of no sensory difference if one exists and if preference is overwhelmingly in one direction.     

Categorical time production: evidence for discrete timing in motor control.

Subjects performed a repetitive manual tapping task, attempting to match a given rate of auditory stimulus pulses, first with the pulses audible (synchronization) and then with the pulses turned off (continuation). In different sessions, the interstimulus interval (ISI) was selected from the range 175 to 825 msec in steps of 25 msec, with different ISI values presented in a random order. Across this range of ISI conditions, interresponse intervals (IRIs) exhibited alternating positive bias (too slow) and negative bias (too fast). We interpret this pattern of bias in terms of a discrete, or categorical, timing mechanism in motor timing. Categorical time production can be viewed as extending our conception of the timekeeper in Wing's (Wing & Kristofferson, 1973a, 1973b) two-process model of motor timing and may be related to the system of multiple clocks proposed by Kristofferson (1980) to explain a categorical pattern of variability measures in duration discrimination.     

Effects of reinforcer delays on choice as a function of income level

Three rats earned their daily food ration by responding during individual trials either on a lever that delivered one food pellet immediately or on a second lever that delivered three pellets after a delay that was continuously adjusted to ensure substantial responding to both alternatives. Choice of the delayed reinforcer increased when the number of trials per session was reduced. This result suggests that models seeking closure on choice effects must include a parameter reflecting how preference changes with sessionwide income. Moreover, models positing that reinforcer probability and immediacy (1/delay) function equivalently in choice are called into question by the finding that probability and immediacy produce opposing effects when income level is changed.