Some effects of later-occurring information on the perception of stop consonant and semivowel

In three experiments, we determined how perception of the syllable-initial distinction between the stop consonant [b] and the semivowel [w], when cued by duration of formant transitions, is affected by parts of the sound pattern that occur later in time. For the first experiment, we constructed four series of syllables, similar in that each had initial formant transitions ranging from one short enough for [ba] to one long enough for [wa], hut different in overall syllable duration. The consequence in perception was that, as syllable duration increased, the [b-w] boundary moved toward transitions of longer duration. Then, in the second experiment, we increased the duration of the sound by adding a second syllable, [da], (thus creating [bada-wada]), and observed that lengthening the second syllable also shifted the perceived [b-w] boundary in the first syllable toward transitions of longer duration; however, this effect was small by comparison with that produced when the first syllable was lengthened equivalently. In the third experiment, we found that altering the structure of the syllable had an effect that is not to be accounted for by the concomitant change in syllable duration: lengthening the syllable by adding syllable-final transitions appropriate for the stop consonant [d] (thus creating [bad-wad]) caused the perceived [b-w] boundary to shift toward transitions of shorter duration, an effect precisely opposite to that produced when the syllable was lengthened to the same extent by adding steady-state vowel. We suggest that, in all these cases, the later-occurring information specifies rate of articulation and that the effect on the earlier-occurring cue reflects an appropriate perceptual normalization.     

Cognitive influences on perceptual processing

These experiments investigate the influence of frequency of occurrence of a visual stimulus (stimulus probability) on encoding processes, in an attempt to discover what sorts of mechanisms allow cognitive processes to modify perceptual processes. Experiments 1 and 2 show that frequently occurring visual letters do not facilitate encoding of visually similar letters. This implies that stimulus probability does not directly affect the feature detectors used in encoding the letters. Four more experiments provide evidence that stimulus probability has its effect on the availability of an abstract code that is generated by the encoding process from the visual input. Results from the experiments with letter stimuli could be interpreted using a model similar to the logogen model of Morton. Experiments with nonsense forms suggest that subjects use abstract codes in dealing with the forms only when the stimuli are constructed from a set of orthogonal features. A secondary finding was that visual quality has an effect that extends past the feature analysis stage and into a stage in which the visual input activities an abstract code. This result calls into question the common practice of interpreting the interaction of a factor with visual quality as evidence that the factor affects visual feature analysis.     

Social Density and Affiliative Tendency as Determinants of Dormitory Residential Outcomes

The questionnaire responses of both high social density and low social density dormitory residents, divided into high and low groups on affiliative tendency, were examined. Although both high and low affiliates experienced more satisfaction living in low social density dorms, which were associated with higher levels of social interaction than high social density dorms, levels of reported stress varied as a function of both social density and affiliation. High affiliates experienced more, while low affiliates experienced less, stress in the low social density dorm than in the high social density dorm. Results were discussed in terms of the possession of differential coping skills with respect to achieving independence (in the low social density dorm) and dealing with overload from strangers (in the high social density dorm).     

Perceptual independence of the hemifields in children and adults

Second graders, fifth graders, and college students were shown words and letters under conditions designed to assess the extent to which stimuli presented to one hemifield and consequently one hemisphere are affected by stimuli projected to the other hemifield. Hemifield, and by implication, hemispheric independence was more likely to occur for letters and among the children, and in each case hemifield asymmetries in performance were also less pronounced. These results were discussed in terms of developmental models of perceptual asymmetry and hemispheric interaction.     

Effects of instructional constraints on human fixed-interval performance

Several groups of human subjects were exposed to a variety of experimental conditions involving a fixed-interval 27-second schedule of reinforcement in compound with instructions to constrain in the number of responses within the interreinforcement interval and/or the duration of the experimental session. One group was further exposed to a contingency involving the placement of responses within the IRI. A diversity of patterns of performance was observed, including those typically associated with animal subjects exposed to FI schedules. Generally, the imposition of instructions to minimize session duration reduced post-reinforcement pausing and increased overall reinforcement density from those levels obtained with only instructions to expend a given number of responses per reinforcer. The results are seen to underscore the sensitivity of human fixed-interval performance and the contribution of extra-experimental contingencies.     

A jackknife test of homogeneity of variance with paired replicates data

A nonparametric test of dispersion with paired replicates data is described which involves jackknifing logarithmic transformations of the ratio of variance estimates for the pre- and post-treatment populations. Results from a Monte Carlo simulation show that the test performs well underH _o and has good power properties. Examples are given of applying the procedure on psychiatric data.A referee called our attention to valuable references which related to our work, and he suggested the inclusion of competing jackknife procedures into our studies.     

Case specificity of the stimulus probability effect

Four memory scanning experiments investigated the effect of the probability of occurrence of one case of a letter (e.g., “A”) on response time to the other case of that same letter (“a”). There was no effect: Responses to one case of a letter did not depend on the probability of occurrence of the other case of the letter. This finding indicates that facilitation of visual encoding by high probability of occurrence is not caused by increased activation at the level of the name code. Previous results rule out the possibility that facilitation occurs at the level of feature detectors responding to the individual visual features of the high-probability stimuli, and these results were replicated in the present experiments. It appears that facilitation is caused by activation along specific routes by which visual features activate letter names. This conclusion has implications for the locus of effect of stimulus probability in models of letter coding     

Somatic and autonomic indexes of recovery from electroconvulsive shock-induced amnesia in rats

Autonomic response indexes of experimental amnesia have recently been found to have higher electroconvulsive shock (ECS) intensity thresholds and steeper retrograde gradients than have traditional somatic indexes. The present studies examined the hypothesis that recovery from somatically indexed experimental amnesia depends upon the existence of autonomically available residual memory. In a between-subjects design, a 200-mA ECS was used to produce amnesia for a tone-footshock pairing as indicated by lick suppression, defection, and bradycardia. The next day, these amnesic animals received a reminder footshock outside of the training apparatus, which was found to restore memory on a test trial 24 hr later. The behavior of control groups indicated that this reminder effect was due to the restoration of specific memory rather than systemic consequences of treatment. With a within-subjects design, a second experiment obtained a reminder effect in animals individually shown to be "fully" amnesic by all three response indexes monitored. A third experiment varied the intensity of the reminder footshock and revealed that the different memory indexes examined do not have reminder-footshock thresholds inversely related to their initial resistance to amnesia. The results support a retrieval-failure view of experimental amnesia and suggest that the same fundamental physiological processes underlie both autonomically indexed memory and somatically indexed memory.