The development of depth perception from motion parallax in infancy

North Dakota State University, Fargo, North Dakota Little is known about infants' perception of depth from motion parallax, even though it is known that infants are sensitive both to motion and to depth-from-motion cues at an early age. The present experiment assesses whether infants are sensitive to the unambiguous depth specified by motion parallax and, if so, when this sensitivity first develops. Eleven infants were followed longitudinally from 8 to 29 weeks. Infants monocularly viewed a translating Rogers and Graham (1979) random-dot stimulus, which appears as a corrugated surface to adult observers. Using the infant-control habituation paradigm, looking time was recorded for each 10-sec trial until habituation, followed by two test trials: one using a depth-reversed and one using a flat stimulus. Dishabituation results indicate that infants may be sensitive to unambiguous depth from motion parallax by 16 weeks of age. Implications for the developmental sequence of depth from motion, stereopsis, and eye movements are discussed.     

Average group behavior does not represent individual behavior in classical conditioning of the honeybee

Conditioned behavior as observed during classical conditioning in a group of identically treated animals provides insights into the physiological process of learning and memory formation. However, several studies in vertebrates found a remarkable difference between the group-average behavioral performance and the behavioral characteristics of individual animals. Here, we analyzed a large number of data (1640 animals) on olfactory conditioning in the honeybee (Apis mellifera). The data acquired during absolute and differential classical conditioning differed with respect to the number of conditioning trials, the conditioned odors, the intertrial intervals, and the time of retention tests. We further investigated data in which animals were tested for spontaneous recovery from extinction. In all data sets we found that the gradually increasing group-average learning curve did not adequately represent the behavior of individual animals. Individual behavior was characterized by a rapid and stable acquisition of the conditioned response (CR), as well as by a rapid and stable cessation of the CR following unrewarded stimuli. In addition, we present and evaluate different model hypotheses on how honeybees form associations during classical conditioning by implementing a gradual learning process on the one hand and an all-or-none learning process on the other hand. In summary, our findings advise that individual behavior should be recognized as a meaningful predictor for the internal state of a honeybee--irrespective of the group-average behavioral performance.     

The interplay between stereopsis and structure from motion

In a series of psychophysical experiments, an adaptation paradigm was employed to study the influence of stereopsis on perception of rotation in an ambiguous kinetic depth (KD) display. Without prior adaptation or stereopsis, a rotating globe undergoes spontaneous reversals in perceived direction of rotation, with successive durations of perceived rotation being random variables. Following 90 sec of viewing a stereoscopic globe undergoing unambiguous rotation, the KD globe appeared to rotate in a direction opposite that experienced during the stereoscopic adaptation period. This adaptation aftereffect was short-lived, and it occurred only when the adaptation and test figures stimulated the same retinal areas, and only when the adaptation and test figures rotated about the same axis. The aftereffect was just as strong when the test and adaptation figures had different shapes, as long as the adaptation figure contained multiple directions of motion imaged at different retinal disparities. Nonstereoscopic adaptation figures had no effect on the perceived direction of rotation of the ambiguous KD figure. These results imply that stereopsis and motion strongly interact in the specification of structure from motion, a result that complements earlier work on this problem.     

Disruption of eye movements by ethanol intoxication affects perception of depth from motion parallax

Motion parallax, the ability to recover depth from retinal motion generated by observer translation, is important for visual depth perception. Recent work indicates that the perception of depth from motion parallax relies on the slow eye movement system. It is well known that ethanol intoxication reduces the gain of this system, and this produces the horizontal gaze nystagmus that law enforcement's field sobriety test is intended to reveal. The current study demonstrates that because of its influence on the slow eye movement system, ethanol intoxication impairs the perception of depth from motion parallax. Thresholds in a motion parallax task were significantly increased by acute ethanol intoxication, whereas thresholds for an identical test relying on binocular disparity were unaffected. Perhaps a failure of motion parallax plays a role in alcohol-related driving accidents; because of the effects of alcohol on eye movements, intoxicated drivers may have inaccurate or inadequate information for judging the relative depth of obstacles from motion parallax.     

Real-time color-frame animation for visual psychophysics on the Macintosh computer

Psychophysical experiments involving moving stimuli require the rapid presentation of animated sequences of images. Although the Macintosh computer is widely used as a color graphics computer in research laboratories, its animation capabilities are generally ignored because of the speed limitations of drawing to the screen. New off-screen color graphics structures help to avoid the speed limitations so that real-time color or gray-scale visual motion stimuli may be generated. Precomputed animation frames are stored in off-screen memory and then rapidly transferred to the screen sequentially. The off-screen graphics structures may also be saved to disk in “Picture” form as “resources” for later retrieval and playback, allowing the experimenter to build in advance a collection of moving stimuli to use in future experiments. Code examples in the C programming language are provided, and the relative strengths and weaknesses of Macin-tosh color-frame animation for psychophysical experimentation are discussed.     

Software for the generation and display of random-dot cinematograms on the Macintosh computer

The software packageDotMovie 1.3.8 was designed to create and display dynamic random-dot cinematograms for studies of motion perception on Macintosh II microcomputers. In each frame of the cinematogram, some dots move in random uncorrelated directions, while other dots move with constant speed in one direction. As the relative number of dots moving in a correlated direction increases, the observer sees flow in the direction of the movement. The software described facilitates the creation of random-dot cinematograms, their presentation, and collection of data from subjects’ responses.     

Expansion of Genetic Services Utilizing a General Genetic Counseling Clinic

We established a general genetic counseling clinic (GCC) to help reduce long wait times for new patient appointments and to enhance services for a subset of patients. Genetic counselors, who are licensed in Tennessee, were the primary providers and MD geneticists served as medical advisors. This article describes the clinic referral sources, reasons for referral and patient dispositions following their GCC visit(s). We obtained patients by triaging referrals made to our medical genetics division. Over 24 months, our GCC provided timely visits for 321 patients, allowing the MD geneticists to focus on patients needing a clinical exam and/or complex medical management. Following their GCC visit(s), over 80 % of patients did not need additional appointments with an MD geneticist. The GCC allowed the genetic counselor to spend more time with patients than is possible in our traditional medical genetics clinic. Patient satisfaction surveys (n?=?30) were very positive overall concerning the care provided. Added benefits for the genetic counselors were increased professional responsibility, autonomy and visibility as health care providers. We conclude that genetic counselors are accepted as health care providers by patients and referring providers for a subset of clinical genetics cases. A GCC can expand genetic services, complement more traditional genetic clinic models and utilize the strengths of the genetic counselor health care provider.