Monte Carlo studies in nonmetric scaling

In response to Arabie several random ranking studies are compared and discussed. Differences are typically very small, however it is noted that those studies which used arbitrary configurations tend to produce slightly higher stress values. The choice of starting configuration is discussed and we suggest that the use of a principal components decomposition of the doubly centered matrix of dissimilarities, or some transformation thereof, will yield an initial configuration which is superior to a randomly chosen one.This research was supported by the National Research Council of Canada (Grant No. A8351) and by the National Institute of Mental Health (Grant Nos. MH10006 and MH26504). The authorship order has been determined by Monte Carlo methods.     

An investigation of the interaural time difference threshold for speech

The interaural time difference threshold for speech has been reported to be approximately 35 μsec (Cherry & Sayers, 1956), a value substantially larger than the 6 ~sec reported for broadband noise signals by other experimenters (e.g., Tobias & Zerlin, 1959). In the two studies just mentioned, however, different subjects and psychoacoustical methods were employed; thus, it is unclear whether larger interaural time differences are needed to lateralize speech signals. The purpose of this experiment, therefore, was to compare lateralization performance for speech and nonspeech stimuli. Interaural time difference thresholds were obtained for speech, speech spectrum noise, speech multiplied noise, and 200-, 500-, and 1,000-Hz sinusoids for the same subjects using a 2 IFC experimental paradigm. Under these conditions, speech and speech-multiplied noise yielded essentially the same interaural time difference thresholds.     

Comments on the interpretation of lateral asymmetries in the naming of words and line drawings

Young, Bion, and Ellis (Brain and Language, 11, 54-65, 1980) found no visual hemifield differences for right-handed subjects' first reports of bilaterally presented picturable nouns and line drawings, and small RVF superiorities for second reports of these stimuli. Levine and Banich (1982), however, found no visual hemifield differences for line drawings, and a substantial RVF superiority for picturable words. Two procedural factors are identified as responsible for this difference in results; namely the lack of control of order of report in Levine and Banich's (1982) study, and their use of vertically aligned words. Levine and Banich's (1982) attempt to explain findings of side of presentation X report interactions in terms of directional scanning and reporting preferences is shown to be untenable. Explanations in terms of cerebral asymmetries are more convincing, but they must be related to explicit theoretical models.     

The effect of repetition on search through active memory

Short lists of digits, some of which contained repeated items, were searched in memory. Repeated items were recognized faster than non-repeated items. Search times for non-repeated items in lists with a repeat were slightly faster than those for lists of the same length in which no items were repeated. A serial position effect was found such that items at either the beginning or end of the memory list were responded to faster than items in the middle of the list. Neither the repeated digit effect nor the serial position effect support serial exhaustive search. An empirical equation was found by which response time is predicted by the log proportion of items in a memory list that match the test stimulus. These results are compatible with the notions of neural pathway activation and trace strength.     

On the origin of personal causal theories

Detecting the causal relations among environmental events is an important facet of learning. Certain variables have been identified which influence both human causal attribution and animal learning: temporal priority, temporal and spatial contiguity, covariation and contingency, and prior experience. Recent research has continued to find distinct commonalities between the influence these variables have in the two domains, supporting a neo-Humean analysis of the origins of personal causal theories. The cues to causality determine which event relationships will be judged as causal; personal causal theories emerge as a result of these judgments and in turn affect future attributions. An examination of animal learning research motivates further extensions of the analogy. Researchers are encouraged to study real-time causal attributions, to study additional methodological analogies to conditioning paradigms, and to develop rich learning accounts of the acquisition of causal theories.     

Enhanced Hippocampal CA1 LTP but Normal Spatial Learning in Inositol 1,4,5-trisphosphate 3-kinase(A)-Deficient Mice

To define the physiological role of IP₃3-kinase(A) in vivo, we have generated a mouse strain with a null mutation of the IP₃3-kinase(A) locus by gene targeting. Homozygous mutant mice were fully viable, fertile, apparently normal, and did not show any morphological anomaly in brain sections. In the mutant brain, the IP₄ level was significantly decreased whereas the IP₃ level did not change, demonstrating a major role of IP₃3-kinase(A) in the generation of IP₄. Nevertheless, no significant difference was detected in the hippocampal neuronal cells of the wild-type and the mutant mice in the kinetics of Ca²⁺ regulation after glutamate stimulation. Electrophysiological analyses carried out in hippocampal slices showed that the mutation significantly enhanced the LTP in the hippocampal CA1 region, but had no effect on the LTP in dentate gyrus (DG). No difference was noted, however, between the mutant and the wild-type mice in the Morris water maze task. Our results indicate that IP₃3-kinase(A) may play an important role in the regulation of LTP in hippocampal CA1 region through the generation of IP₄, but the enhanced LTP in the hippocampal CA1 does not affect spatial learning and memory.     

GENERALIZED IMITATION AND RESPONSE-CLASS FORMATION IN CHILDREN WITH AUTISM

An experimental analysis of imitation was conducted to examine the influence of response topography on generalization of imitation across three response types. Four children with autism were presented with both reinforced training trials and nonreinforced probe trials of models from vocal, toy-play, and pantomime response types. The probe trials were used to examine generalization within each response type. A multiple baseline design was used to analyze percentage of matching and nonmatching responses to models across response types. This study, the first to analyze imitative response classes in children with autism, showed that imitation generalized from reinforced training models to nonreinforced probe models within a response type, but it did not generalize across response types. Thus, functional response classes determined by topographical boundaries were exhibited within generalized imitation.