Perception of translational heading from optical flow

Radial patterns of optical flow produced by observer translation could be used to perceive the direction of self-movement during locomotion, and a number of formal analyses of such patterns have recently appeared. However, there is comparatively little empirical research on the perception of heading from optical flow, and what data there are indicate surprisingly poor performance, with heading errors on the order of 5 degrees-10 degrees. We examined heading judgments during translation parallel, perpendicular, and at oblique angles to a random-dot plane, varying observer speed and dot density. Using a discrimination task, we found that heading accuracy improved by an order of magnitude, with 75%-correct thresholds of 0.66 degrees in the highest speed and density condition and 1.2 degrees generally. Performance remained high with displays of 63-10 dots, but it dropped significantly with only 2 dots; there was no consistent speed effect and no effect of angle of approach to the surface. The results are inconsistent with theories based on the local focus of outflow, local motion parallax, multiple fixations, differential motion parallax, and the local maximum of divergence. But they are consistent with Gibson's (1950) original global radial outflow hypothesis for perception of heading during translation.     

A revision of the definition of lying as an untruth told with intent to deceive

The traditional and prevailing definition of lying is that lying is some variation or combination of: an untruth told with intent to deceive. I establish that this is the case, and that, as a result, contradictions and injustices arise. An alternative definition is proposed which is shown to avoid these difficulties. It is also shown that and how on the new definition the alleged Liar paradox is easily dissolved.     

Evidence for an error deadzone in compensatory tracking

Humans and monkeys show intermittent arm movements while tracking moving targets. This intermittency has been explained by postulating either a psychological refractory period after each movement and/or an error deadzone, an area surrounding the target within which movements are not initiated. We present a technique to detect and quantify the size of this deadzone, using a compensatory tracking paradigm that distinguishes it from a psychological refractory period. An artificial deadzone of variable size was added around a visual target displayed on a computer screen. While the subject was within this area, he received visual feedback that showed him to be directly on target. The presence of this artificial deadzone could affect tracking performance only if it exceeded the size of his intrinsic deadzone. Therefore, the size of artificial deadzone at which performance began to be affected revealed the size of the intrinsic deadzone. Measured at the subjects' eye, the deadzone was found to vary between 0.06 and 0.38 degrees, depending on the tracking task and viewing conditions; on the screen, this range was 1.3 mm to 3.3 mm. It increased with increasing speed of the target, with increasing viewing distance, and when the amplitude of the movement required was reduced. However, the deadzone size was not significantly correlated with the subjects' level of performance. We conclude that an intrinsic deadzone exists during compensatory tracking, and we suggest that its size is set by a cognitive process not simply related to the difficulty of the tracking task.     

The role of central and peripheral vision in perceiving the direction of self-motion.

Three experiments were performed to examine the role that central and peripheral vision play in the perception of the direction of translational self-motion, or heading, from optical flow. When the focus of radial outflow was in central vision, heading accuracy was slightly higher with central circular displays (10 degrees-25 degrees diameter) than with peripheral annular displays (40 degrees diameter), indicating that central vision is somewhat more sensitive to this information. Performance dropped rapidly as the eccentricity of the focus of outflow increased, indicating that the periphery does not accurately extract radial flow patterns. Together with recent research on vection and postural adjustments, these results contradict the peripheral dominance hypothesis that peripheral vision is specialized for perception of self-motion. We propose a functional sensitivity hypothesis--that self-motion is perceived on the basis of optical information rather than the retinal locus of stimulation, but that central and peripheral vision are differentially sensitive to the information characteristic of each retinal region.     

Increasing the intelligibility of speech through multiple phonemic restorations

Outside of the laboratory, listening conditions are often less than ideal, and when attending to sounds from a particular source, portions are often obliterated by extraneous noises. However, listeners possess rather elegant reconstructive mechanisms. Restoration can be complete, so that missing segments are indistinguishable from those actually present and the listener is unaware that the signal is fragmented. This phenomenon, called temporal induction (TI), has been studied extensively with nonverbal signals and to a lesser extent with speech. Earlier studies have demonstrated that TI can produce illusory continuity spanning gaps of a few hundred milliseconds when portions of a signal are replaced by a louder sound capable of masking the signal were it actually present. The present study employed various types of speech signals with periodic gaps and measured the effects upon intelligibility produced by filling these gaps with noises. Enhancement of intelligibility through multiple phonemic restoration occurred when the acoustic requirements for TI were met and when sufficient contextual information was available in the remaining speech fragments. It appears that phonemic restoration is a specialized form of TI that uses linguistic skills for the reconstruction of obliterated speech.     

Actions, intentions, and consequences: the doctrine of double effect

One interpretation of the doctrine of double effect (DDE) holds that in situations in which good can be secured for some only if others suffer harm, the pursuit of a good tends to be less acceptable when a resulting harm is intended as a means rather than when it is merely foreseen. The doctrine captures certain moral intuitions about pairs of cases which have the same consequential profiles but in which the character of the intention differs. Quinn examines the DDE using three pairs of contrasting cases, two of which are medical examples: the "Direction of Resources" case and the "Guinea Pig" case, both involving allocation of life-saving resources, and the "Craniotomy" case and the "Hysterectomy" case, both involving fetal vs. maternal life. He concludes that the DDE "embodies our sense that certain forms of forced strategic subordination are especially inappropriate among free and equal agents."     

Further validity and normative data for the Malouff and Schutte belief scale

The present study provides further validity and normative data for the Malouff and Schutte (1986) Belief Scale. Belief Scale, Eysenck Personality Questionnaire-Neuroticism Scale, and Beck Depression Inventory scores of a sample of 197 adults were correlated, and evidence for both construct and discriminant validities and support for the RET model were obtained. The Belief Scale appears to be a promising instrument for clinical research and the assessment of irrational beliefs.Ricks Warren, Ph.D. is the Director of the Anxiety Disorders Clinic, Lake Oswego, Oregon, and Associate Clinical Professor at the Oregon Graduate School of Professional Psychology, Pacific University. George D. Zgourides, M.A., is a doctoral student in clinical psychology at Pacific University of Forest Grove, Oregon and an associate therapist at the Anxiety Disorders Clinic of Lake Oswego, Oregon.     

Cognitive bias and irrational belief as predictors of avoidance

Cognitive bias, i.e. overestimates of subjective probability and cost of catastrophic events, and irrational belief were explored as predictors of avoidance. Three groups-anxiety disordered clients, a mixed group of clinic outpatients, and normals--were administered several self-report inventories. Multiple regression analyses were used to investigate a modified version of the Agoraphobic Cognitions Questionnaire, the Belief Scale, and the Body Sensations Questionnaire as predictors of avoidance, as measured by the Mobility Inventory. It was hypothesized that frequency x probability x cost of catastrophic cognitions (and the occurrence of the events they represent) would be a better predictor of avoidance than frequency alone. It was also hypothesized that irrational thinking would be a significant predictor of avoidance. The results generally supported the hypotheses, with subjective probability emerging as a particularly potent predictor of avoidance. Theoretical and clinical implications are discussed.