Harold P. Bechtoldt

Dominance of the right cerebral hemisphere for stereopsis

Abstract Patients with unilateral right hemispheric lesions exhibited marked deficits in performance (more errors and longer response times) relative to patients either with unilateral left hemispheric lesions or with no brain damage on stereoscopically presented stimuli in a task requiring the location of a form in depth from binocular disparity cues without the aid of figure-ground contours or of monocular cues of form and depth. The stimuli were modifications of the random dot stereograms developed by B. Julesz. No deficits in the performance of the left hemisphere patients were found. The results are consistent with the hypothesis of relative dominance of the right hemisphere for stereopsis in the absence of monocular cues of form and depth.

An empirical study of the factor analysis stability hypothesis

Note is taken of four related sources of confusion as to the usefulness of Thurstones factor analysis model and of their resolutions. One resolution uses Tuckers distinction between exploratory and confirmatory analyses. Eight analyses of two sets of data demonstrate the procedures and results of a confirmatory study with statistical tests of some, but not all, relevant hypotheses in an investigation of the stability (invariance) hypothesis. The empirical results provide estimates, as substitutes for unavailable sampling formulations, of effects of variation in diagonal values, in method of factoring, and in samples of cases. Implications of these results are discussed.

Binocular integration in line rivalry

Three experiments investigated the frequency of a monocular, partial binocular, or nearly total binocular report of dichoptically presented stimuli in a line rivalry paradigm. The consistently important variable was the duration of the presentation time of the stimuli, which ranged from 50 to 1,100 msec, with each experiment covering only a portion of these times. Variations in equipment, instructions, response mode, light intensity, and position in the visual field were introduced. The main result was a report of fusion of the binocular inputs, with little or no suppression for about 40% to about 80% of the foveal presentations of 100 msec or less, the percentage varying over the three experiments. Partial fusion (some, but not all, lines crossed) was indicated in another 40% or more of the reports. Lateral positioning of the stimuli 6 deg from the fixation point, but not at 3 deg or less, resulted mainly in reports of monocular inputs. The possibility, and serious implication for studies of rivalry phenomena, of range effects (Poulton) from the within-subjects variation of duration of stimuli was noted.

Factor Analysis and the Investigation of Hypotheses

Experimental and Statistical Issues 320 ......... Statement of Hypotheses 32 1 ..... First Issue: Starus Differences and Factor Analysis 323 Second Issue: Definition of Ability Variables 324 Third Issue: Factor Procedures in Definitions ........................................................ 324 . . . Fourth ,Issue: Indices of Rela t~onsh~p 325 .. Resolut~on of the Issues 330 Sequential Application of Two Methods of Analysis 332 Data 332 Procedures 332 Analysis and Results 333 ....... Adequacy of Seven Factors 333 . Regression Analysis With Seven Predictors 335 Regression Analysis Wi th Nine . Predictors . 336

Visual recognition as a function of stimulus offset asynchrony and duration

The stimuli consisted of two complementary dot patterns that formed a bigram when they were flashed simultaneously; impairment of letter recognition developed when one of the patterns was briefly extended beyond the termination of the other (stimulus offset asynchrony). However, if the ratio of stimulus offset asynchrony to bigram duration remained constant, the probability of a correct recognition response also remained constant as duration varied over a 50- to 100-msec interval. When percent stimulus asynchrony increased, the impairment increased. An interaction between bigram letter position and each of bigram duration and percent stimulus asynchrony was observed with recognition accuracy greater in general for the letter in the left half of the field.

Categorical perception of stereoscopic stimuli

Two studies of the stereopsis model of Richards were conducted using a between-subjects balanced design and a repeated trials procedure rather than the within-subjects procedure of Richards. Measures of the accuracy of discrimination between classes of retinal disparity were defined by the method of successive intervals in place of the d’ index of SDT. The results support the predictions (1) of symmetric discrimination functions for convergent and divergent stimuli, (2) of greater discrimination for stimuli of 45 min of retinal disparity than for the stimuli of 15 min disparity, (3) of greater variability for the stimuli of greater disparity, and (4) of the use by nonanomalous subjects of at least two different processing mechanisms for stimuli of different disparity classes. The results do not support the prediction (1) of different processing mechanisms for foveal stimuli differing in figure-ground contrast or (2) of greater usefulness for monocular stimuli as a null disparity reference condition, as compared with binocular null disparity stimuli. Similar results were found for two stimulus shapes, a bar and a disk of equal area. Unreliability of subjects’ response systems was suggested as a factor in the prediction of figure-ground contrast changes and as a factor in the classification of subjects as stereo anomalous. The pattern of accuracy of discrimination between classes of disparity stimuli also raises questions of the adequacy of the simple stereopsis model.

A Confirmatory Analysis of the Factor Stability Hypothesis.

The procedures recently developed by Jöreskog for studying similarities and differences in factor structures between different groups were applied to data from a study designed by Thurstone to investigate the sampling stability of a hypothesized isolated configuration. The hypothesis of an isolated configuration was rejected but not by much. The results represent a restricted and unique simple structure solution with the factor loadings and uniqueness values invariant over the two samples.

Correlational methods in research on human learning: an amplification.

This paper considers two recommendations regarding the use of correlational methods in research on problems of human learning. These suggestions are that residual gain scores are especially appropriate for defining gains in such studies and that the results of factor analyses of gain scores are relevant to substantive problems of learning. It is concluded, first, that no acceptable logical or empirical grounds were presented for preferring residual scores to other linearly defined gain scores for use with correlational techniques; instead, the residual scores were shown to have several serious weaknesses. The second conclusion is that a factor analysis of gain scores is inappropriate for substantive problems of human learning; however, properly designed and correctly analyzed factor studies may supplement other techniques for such problems. Some weaknesses of a single-group design for a study of learning effects were also noted.

The development of binocular discrimination in infants

The ability of 8- to 13-week-old infants to discriminate between stereoscopic and non-stereoscopic stimuli under short habituation experiences was tested repeatedly until they were 24 weeks old or able to reach for real objects with direction of gaze to one of two adjacent displays of a shadow-caster as the criterion measure. Stereopsis was demonstrated at the final session in 83% of the subjects by a reaching response to a virtual image. All but 1 of the 26 subjects discriminated on every test between depth and no-depth stimuli with no age differential; the subjects generally preferred the no-depth stimulus. While stereopsis and reactions to novelty or to complexity are possibile explanations of shadow-caster discriminations, the significant reaching response results plus the consistent gaze preference strongly support the hypothesis that binocular functioning is available at 8 weeks of age.