Classical geometric illusion effects with nonclassical stimuli: Angular induction from decomposing lines into point arrays

Angular induction is the process by which one line segment can bias judgment of orientation and/or collinearity of another segment, and it has been established that the magnitude of error is a determinate function of the relative angle between the two. We examined how these known relationships are affected by decomposing the induction segment into an array of scattered points. The bias that was produced by such arrays was found to be consistent with a formal model of angular induction, with the strength of the effect decreasing as the scatter among the points was increased. This decline in strength was almost linear with a logarithmic transform of the dimensions of the stimulus array. We also evaluated the hypothesis that the induction stimulus is detected by one or more channels—for example, neurons—for which the sensitivity profiles are modeled as Gabor wavelets. The change in induction strength with increasing point scatter was not predicted by a single width of channel. However, the combined activity of an ensemble of channels that differed in width did match the perceptual effects if one also stipulated that each channel would respond maximally to a fine-line stimulus.     

Local and global factors of similarity in visual search

Effects of the similarity between target and distractors in a visual search task were investigated in several experiments. Both familiar (numerals and letters) and unfamiliar (connected figures in a 5 × 5 matrix) stimuli were used. The observer had to report on the presence or absence of a target among a variable number of homogeneous distractors as fast and as accurately as possible. It was found that physical difference had the same clear effect on processing time far familiar and for unfamiliar stimuli: processing time decreased monotonically with increasing physical difference. Distractors unrelated to the target and those related to the target by a simple transformation (180° rotation, horizontal or vertical reflection) were also compared, while the physical difference was kept constant. For familiar stimuli, transformational relatedness increased processing time in comparison with that fort unrelated stimulus pairs. It was further shown in a scaling experiment that this effect could be accounted for by the amount of perceived similarity of the target-distractor pairs. For unfamiliar stimuli, transformational relatedness did have a smaller and less pronounced effect. Various comparable unrelated distractors resulted in a full range of processing times. Results from a similarity scaling experiment correlated well with the outcome of the experiments with unfamiliar stimuli. These results are interpreted in terms of an underlying continuum of perceived similarity as the basis of the speed of visual search, rather than a dichotomy of parallel versus serial processing.     

Communicative behavior of mothers of stuttering and nonstuttering high-risk children prior to the onset of stuttering

This portion of a multiyear prospective study was designed to investigate the communicative style, speaking rate, and language complexity of 93 mothers of preschool children with a parental history of stuttering. At the initial session none of the children sampled was regarded as being a stutterer. One year later, 26 of the children were classified as stutterers. Statistical analyses revealed that prior to the onset of stuttering the mothers of these children did not differ from the mothers of the children who continued to be seen as nonstutterers with respect to either communicative style or speaking rate. The only significant difference between the two groups of mothers was the complexity of their language. The pre-onset mean lengths of utterance (MLUs) of the mothers of children who later came to be regarded as stutterers were significantly shorter than those of the mothers whose children continued to be viewed as being fluent. These findings suggest that the communicative behavior of mothers of normally fluent children do not contribute to the development of stuttering.     

Sparing and recovery of function in spinal larval frogs (Rana catesbeiana): effect of level of transection.

Bullfrog tadpoles with cervical or midthoracic transection of the spinal cord were allowed to recover for 5 weeks, at which time axonal growth across the transection site was assessed by transport of horseradish peroxidase. Weekly behavioral tests included those for posture, spontaneous locomotion, cutaneously elicited swimming, and intersegmental coordination. Behavioral and electrophysiological assessments suggest that behavioral recovery depends, at least in part, on the growth of fibers across the transection site. Anatomical and behavioral recovery does not appear to differ with the level of spinal transection, but there was greater sparing of posture, spontaneous locomotion, and stimulus-induced locomotion in tadpoles with thoracic transection of the spinal cords.