Psychophysical functions for active tactual discrimination of line width by blind children

Two psychophysical experiments were conducted on active tactual discrimination of line width using the method of constant stimuli with blind subjects. In Experiment I, 93 subjects made single judgments over each of five standards between 0.04 and 0.12 in. In Experiment II, 6 subjects were tested repeatedly over seven standards between 0.04 and 0.50 in. Over the range of standards common to both experiments, the Weber fractions decreased as the width of the standard increased. For two larger standards (0.25 and .50 in.), the Weber fractions approached asymptote and then increased respectively suggesting a U-shaped function. No differences in accuracy of discrimination were found between males vs. females, age groupings, or grade groupings.     

Visual form discrimination: Multidimensional analyses

Nonmetric multidimensional scaling techniques were used to evaluate discrimination latency as a similarity measure. A three dimensional Euclidian solution was found for a sample of random polygons. The dimensions were labeled compactness, jaggedness, and elongation. The spatial configuration was highly similar to results obtained from similarity estimates and the dimensions were systematically related to physical shape measures.     

Visual and tactual form complexity:A psychophysical approach to perceptual equivalence

Equivalence of two modalities for processing form-complexity information was investigated by obtaining category judgments of the complexity of 100 random forms from 40 Ss who explored the forms visually and 40 Ss who explored them tactually. Intercorrelations of judgments and multiple regression analyses with form measures indicate that information was used in the same fashion independent of input modality. Latencies were interpreted as reflecting information gaining and processing capabilities.     

Visual and tactual texture perception: Intersensory cooperation

In three experiments, subjects were required to make texture judgments about abrasive surfaces. Touch and vision provided comparable levels of performance when observers attempted to select the smoothest of three surfaces, but bimodal visual and tactual input led to greater accuracy. The superiority of bimodal perception was ascribed to visual guidance of tactual exploration. The elimination of visual texture cues did not impair bimodal performance if vision of hand movements were permitted. It is suggested that touch may preempt vision when both sources of texture information are simultaneously available. The results support the notion that perception is normally multimodal, since restriction of the observer to either sense in isolation produces lower levels of performance.     

Visual discrimination between rectangular and nonrectangular parallelopipeds

Twenty-seven university students judged whether each of 128 drawings of parallelopipeds appeared to represent three-dimensional rectangular boxes. Half the pictures could not geometrically have been projections of rectangular boxes. The null hypothesis that Ss’ judgments were unrelated to geometry was rejected at the .001 level of significance, and the correlation between Ss’ judgments and perfect discrimination averaged .86 over three variations of the experiment. The results support a general hypothesis about the perception of simple space forms according to which viewers impose geometric constraints, such as rectangularity and symmetry, but only when the constraints are projectively possible.     

Task coordination between and within sensory modalities: effects on distraction

Load theory predictions for the effects of task coordination between and within sensory modalities (vision and hearing or vision only) on the level of distraction were tested. Response competition effects in a visual flanker task when it was coordinated with an auditory discrimination task (between-modality conditions) or a visual discrimination task (within-modality conditions) were compared with single-task conditions. In the between-modality conditions, response competition effects were greater in the two- (vs. single-) task conditions irrespective of the level of discrimination task difficulty. In the within-modality conditions, response competition effects were greater in the two-task (vs. single-task) conditions only when these involved a more difficult visual discrimination task. The results provided support for the load theory prediction that executive control load leads to greater distractor interference while highlighting the effects of task modality.     

Visual movement perception: A comparison of absolute and relative movement discrimination

It is proposed that there are two types of visual movement perception, absolute and relative. The former occurs when an object is seen to move in an otherwise homogeneous (or at least locally homogeneous) visual field. Relative judgments occur when one object is seen to move with respect to another, i.e., the separation between them is seen to change. Quantitative models for both processes are developed, and an experiment reported for which the models seem appropriate. The results appear relevant to a theory of size of length perception as well as to the general perceptual issue of absolute and relative judgments.     

Visual masking effects on duration,size, and form discrimination

In duration, size, and form discrimination tasks, a visual noise mask was presented at variable delays after stimulus offset in order to interrupt processing and control the extent of processing time. Previous work (Thomas & Cantor, 1975) had suggested that both perceived duration and perceived nontemporal “information” might be expected to increase as processing time was extended. As predicted, accuracy in the discrimination of size of circles and form of non-sense figures was found to vary directly with stimulus duration (20, 50 msec) and mask delay interval (0, 30, 70, 110 msec). Differences in perceived duration between filled (forms or circles) and unfilled (blank) intervals were found to increase monotonically with increases in the mask delay interval, when non-sense forms, but not circles, were presented. Two hypotheses of visual masking (“integration” and “interruption”) are discussed. Within the context of the “integration” hypothesis, a model is proposed which predicts processing time as a function of stimulus duration, mask delay interval, and the interval between onset of the mask and termination of processing.     

The role of consolidation for perceptual learning in temporal discrimination within and across modalities

Training people on temporal discrimination can substantially improve performance in the trained modality but also in untrained modalities. A pretest–training–posttest design was used to investigate whether consolidation plays a crucial role for training effects within the trained modality and its transfer to another modality. In the pretest, both auditory and visual discrimination performance was assessed. In the training phase, participants performed only the auditory task. After a consolidation interval of either 5 min or 24 h, participants were again tested in both the auditory and visual tasks. Irrespective of the consolidation interval, performance improved from the pretest to the posttest in both modalities. Most importantly, the training effect for the trained auditory modality was independent of the consolidation interval whereas the transfer effect to the visual modality was larger after 24 h than after 5 min. This finding shows that transfer effects benefit from extended consolidation.     

Forewarned is forearmed: Potential between and within sex discrimination

Effects of sex and concern for equal employment opportunity on responses to mailed job applicant resumes were examined. Applicant sex and concern for equal employment opportunity were systematically varied to yield four different resumes for two functionally equivalent applicants. One of the four resumes of the applicants was sent to 200 corporations. Sex of the applicant was identified using a female name and initials (neutral designation). Interest in equal employment opportunity was manipulated using a thesis title involving sex discrimination and no thesis reported. Results indicated that both the number of replies and number of positive responses were influenced by the interaction of an applicant's sex and interest in sex discrimination.     

Statistical learning within and between modalities: pitting abstract against stimulus-specific representations

When learners encode sequential patterns and generalize their knowledge to novel instances, are they relying on abstract or stimulus-specific representations? Research on artificial grammar learning (AGL) has shown transfer of learning from one stimulus set to another, and such findings have encouraged the view that statistical learning is mediated by abstract representations that are independent of the sense modality or perceptual features of the stimuli. Using a novel modification of the standard AGL paradigm, we obtained data to the contrary. These experiments pitted abstract processing against stimulus-specific learning. The findings show that statistical learning results in knowledge that is stimulus-specific rather than abstract. They show furthermore that learning can proceed in parallel for multiple input streams along separate perceptual dimensions or sense modalities. We conclude that learning sequential structure and generalizing to novel stimuli inherently involve learning mechanisms that are closely tied to the perceptual characteristics of the input.