Oculomotor adjustments and size constancy

The effect on matched size of the oculomotor adjustments was determined by stimulation and relaxation of accommodation and convergence by means of spherical lenses. The normal coupling between accommodation and convergence was maintained by introducing the amount of convergence appropriate to the lens power and each S’s interpupillary distance. Data indicate that the oculomotor adjustments are adequate to account for size constancy up to approximately 1 m, beyond which their effect progressively decreases. The actual accommodation in force was assessed by means of the laser scintillation technique. It was determined that the magnitude of accommodation responds accurately to the spherical lens introduced up to about 1 m observation distance, beyond which underaccommodation was noted. Examination of the matched size as a function of the actual accommodation distance reveals a very close correspondence to the size constancy prediction up to about 1 m.     

Laser optometer incorporating the Badal principle

The refractive state of the eye can be accurately determined while performing a visual task by introducing the diverged beam of a laser, reflected from a moving drum, into the visual field. The direction of the apparent motion of the resultant interference pattern is a direct indicator of refractive state. By incorporation of the Badal principle into the optical system, a measurement can be completed within approximately 30 sec. The advantage of this method over other techniques is that it permits evaluation of refractive state but does not itself influehce the magnitude of accommodation. A number of applications of this principle are cited.     

The effect of feedback on luminance thresholds for peripherally presented stimuli

The effect of a central task on peripheral vision was determined by obtaining absolute luminance thresholds for peripherally presented stimuli. A competing central task was provided by interrupting the fixation light and requiring the S to reilluminate it. Data were obtained over five sessions, with feedback information provided on each trial. Thresholds were highest for the initial session and declined as a function of practice. The magnitude of the change depended upon the interruption rate. When central and peripheral stimuli compete for attention, priority is given initially to the central task, but, with practice, the differences are reduced.     

Oculomotor adjustments in darkness and the specific distance tendency

Two experiments were performed to investigate the relationship between the oculomotor adjustments assumed in total darkness and perceived distance under reduced visual conditions. Experiment I compared the dark focus of accommodation with the perceived distance of a monocular light point presented in a dark environment. Experiment II compared the convergence angle assumed in darkness (dark convergence) with the perceived distance of the light point. Both accommodation and convergence were found to assume intermediate values in darkness. Perceived distance of the monocular light point was significantly correlated with dark convergence and unrelated to the dark focus of accommodation. It was suggested that ocular vergence is a major determinant of perceived distance under reduced visual conditions, and thus provides a possible mechanism for the specific distance tendency.     

Limbic system dysfunction and inventoried psychopathology among incarcerated pedophiles

This study explored relationships between “highly probable” neuropathology in the limbic system (as gauged by clinically elevated scores on the Limbic System Check-list-33, or LSCL-33, a screening index for limbic system dysfunction developed by medical researchers at Harvard and Dartmouth) and inventoried psychopathology (as gauged through scores on the MMPI) among a group of adjudicated pedophiles incarcerated for treatment in a specialized prison for criminal sexual psychopaths in a mid-Atlantic state. Principal findings: Only 33 percent of this sample of incarcerated pedophiles exhibits scores on the LSCL-33 at a level high enough to warrant a medical conclusion of “probable” limbic system dysfunction. When scores on the MMPI are grouped according to critical values for clinically relevant scores on the LSCL-33, significant F ratios in one-way analyses of variance are observed on L, F, K, Hs, D, Hy, Pa, Pt, Sc, and Ma. Mean T scores for “probable” dysfunctionals simultaneously reach elevations at or above the threshold of clinical significance for Pd, Pa, and Sc. On that basis, the categorization psychopathic paranoid schizophrenia readily applies to limbic system dysfunctional child sexual abusers studied in this inquiry, but not to their nondysfunctional counterparts. But significant F ratios are observed neither for the age of the victim(s) in the instant offense(s), for the number of prior arrests for sex offenses, for the number of prior arrests for any and all felony offenses, including sex offenses, nor for the offender's current age. However, a stepwise multiple regression between gross number of prior arrests for any and all offenses (including sex offenses) as the most robust of the indices of past criminal activity and both LSCL-33 and MMPI scores across all offenders represented in this inquiry (i.e., the limbic system dysfunctional, the nondysfunctional, and a mid-range group) proceeds to four steps, achieving a multiple R of .575 and encompassing Pd, Mf, Pa, and LSCL-33 scores as the most efficient interactive post-dictive set. Stepwise multiple regression analyses of past arrest record computed independently for limbic system dysfunctionals and nondysfunctionals progresses among dysfunctionals to seven steps, achieving a multiple R of .867 and encompassing Pd, Hy, Ma, Mf, Si, Pa, and Sc scores as the most efficient interactive post-dictive set; and among nondysfunctionals, to six steps, achieving a multiple R of .797 and encompassing Mf, D, Pt, Hy, Pa, and over-controlled hostility scores as the most efficient interactive post-dictive set. The latter results are interpreted as suggesting that neuropathology and psychopathology interact with and potentiate each other in post-dicting criminal behavior among the pedophiles studied in this inquiry. This study was supported in part by the Fund for Correctional and Forensic Psychology, Rutgers University Foundation. The investigators express deep appreciation to Charles Albino for assis-tance in data collection.     

Evidence for the persistence of visual guidance information

An earlier study from our laboratory provided initial support for the hypothesis that information facilitating visual guidance persists in the absence of retinal stimulation. The present study supports and extends this hypothesis with three experiments in which visually occluded subjects positioned a point of light at the location of a previously viewed target and also walked in the direction of a previously viewed path. In both tasks, performance was possible following occlusion, and in all cases, performance slowly and significantly decreased with longer durations of occlusion. This decay in performance was gradual and had a “half-life” of greater than 15 sec. Absolute performance was correlated across tasks. The effect of occlusion on absolute error in the localization performance was relatively stable within individuals over a 3-week period. The biological utility of guidance information persistence is discussed along with implications for space constancy, illusions of motion, and problems of disorientation.     

Age differences in estimating vehicle velocity

Automobile accidents among older adults may be related to difficulties in judging the speed of other vehicles. To examine this possibility, 3 groups of observers in the young adult, middle-aged, and older adult age ranges were asked to estimate the velocity of an isolated automobile traveling at 15-50 mph (24-80 kph). Across all age groups, perceived and actual velocity were related by a power function with an exponent of 1.36. Age was significantly and positively correlated with intercepts, but negatively correlated with exponents; that is, older observers showed less sensitivity to changes in actual velocity. Results bear on the issues of ontogenetic changes in accident involvement and sensitivity to motion.