Visually guided locomotion: psychophysical evidence for a neural mechanism sensitive to flow patterns.

Inspecting a radial flow pattern depressed visual sensitivity to changes in the size of a small test square, but only when the square was located near the focus of the flow pattern. The result suggests that precise visual judgments of one's direction of forward motion with respect to the outside world may be mediated by an already known neural organization sensitive to changes in the size of small objects.

How do we avoid confounding the direction we are looking and the direction we are moving?

Contrary to a previous assumption, the center of the expanding pattern of visual flow is not generally useful as an aid in judging the direction of self motion since its direction depends on the direction of gaze. For some visual environments, however, the point of maximum rate of change of magnification in the retinal image coincides with the direction of self motion, independently of the direction of gaze. This visual indicator could be used to judge the direction of self motion.

Disparity detectors in human depth perception: evidence for directional selectivity.

Viewing a target moving in depth depresses visual sensitivity to depth when test and adapting stimuli simulate motion along closed paths with the same directions of rotation. However, for opposite directions of rotation, sensitivity is either unaffected or increased. This points to two classes of disparity detectors. Either eye's input to a single class of disparity detector consists of the physiological responses to a single direction of horizontal movement.

Patients with multiple sclerosis experience hearing loss specifically for shifts of tone frequency.

After exposure to a prolonged tone of changing intensity but constant frequency, controls, patients with peripheral hearing loss, and patients with multiple sclerosis (MS) demonstrated a reduced sensitivity to shifts in intensity; sensitivity to frequency shifts was unaffected. After exposure to a prolonged tone of changing frequency but constant intensity, control and patients with peripheral hearing loss demonstrated reduced sensitivity to shifts in frequency; sensitivity to intensity shifts was unaffected. Some patients with MS showed no loss of sensitivity to shifts in frequency. Our findings suggest that some patients with MS have abnormal mechanisms for processing changes of frequency. If such processing of frequency change is important for understanding speech, then this observation of a specific central hearing defect may help to explain poor speech discrimination in some patients with MS who have normal audiograms.

Visual fields described by contrast sensitivity, by acuity, and by relative sensitivity to different orientations.

Sinewave grating contrast sensitivity was measured as a function of eccentricity and azimuthal angle for four orientations of gratings whose spatial frequencies ranged from 2 to 20 c/deg. Visual fields for cutoff spatial frequency were also mapped. Log contrast sensitivity fell off approximately linearly with eccentricity for all azimuths. Orientational differences in contrast sensitivity varied irregularly over the visual field and, though small for central vision, could reach as high as 25 dB in localized patches at eccentricities greater than about 12 degrees.

Texture changes versus size changes as stimuli for motion in depth.

As an object approaches the eye, its retinal image size grows larger and its surface texture appears to grow coarser. We compare these two visual correlates of motion in their effectiveness as stimuli for motion in depth. In some experiments texture and object size both expanded or both contracted; in other experiments the two stimuli were pitted against each other. When texture and size change as for a rigid, nonrotating real world object an untextured square can be a more effective stimulus for motion in depth than the same square with texture. On way of describing this finding is to calculate the departure from linear summation of texture and size contributions. The departure is greatest when texture is static, being even greater than when texture changes in the opposite direction to size.

Visual fields for frontal plane motion and for changing size.

Thresholds were measured in 15 subjects for 2-Hz oscillations of size and for 2-Hz oscillatory motion in the frontal plane using test squares of side lengths 0.5 degrees, 1.0 degrees and 2.0 degrees. Size-oscillation thresholds were lowest (i.e. sensitivity was greatest) for the 2.0 degrees square while thresholds were highest (i.e. sensitivity was least) for the 0.5 degrees square in 28 of 34 tests. Frontal plane motion thresholds, on the other hand, did not generally depend on square size. Equal-threshold contours in the visual field were roughly elliptical in 10 of 13 subjects for both types of oscillation. None of 13 subjects had visual field defects for oscillating-size or frontal plane motion, in contrast with the known incidence of stereo-motion scotomata. One subject was known to be selectively "blind" to stereoscopically-oscillating disparity in some areas of the visual field, but oscillating-size sensitivity was normal in these regions, thus preserving an alternative basis for motion-in-depth judgments.

Device for measuring the precision of eye-hand coordination while tracking changing size.

Psychophysical evidence supports the idea that the human visual pathway computes an object's rate of change of angular size rather independently of the object's trajectory and rather independently of other visual parameters, including contrast and intensity. This independence could provide a basis for accurately judging the component of an object's velocity along a line through the eye in the working visual environment where many visual parameters vary simultaneously. We describe a procedure for quantifying a subject's ability to track changing size, and illustrate the procedure with preliminary experimental data. The subject's R.M.S. tracking errors are displayed in three frequency bands. Our device also measures the perturbing effect of sideways motion upon the subject's ability to track changing size. Such data may go some way to predict a subject's performance in tasks of eye-limb coordination, especially where visual information is largely restricted to the changing-size channel.

Correlations between visual test results and flying performance on the advanced simulator for pilot training (ASPT).

Looking for visual differences in pilots to account for differences in flying performance, we tested five groups of subjects: Air Force primary student jet pilots, graduating (T38 aircraft) students, Air Force pilot instructors, and two control groups made up of experienced nonpilot aircrew and nonflying civilians. This interim report compares 13 different visual test results with low-visibility landing performance on the Air Force Human Resources Laboratory ASPT simulator. Performance was assessed by the number of crashes and by the distance of the aircraft from the runway threshold at the time of the first visual flight correction. Our main finding was that, for student pilots, landing performance correlated with tracking performance for a target that changed size (as if moving in depth) and also with tracking performance for a target that moved sideways. On the other hand, landing performance correlated comparatively weakly with psychophysical thresholds for motion and contrast. For student pilots, several of the visual tests gave results that correlated with flying grades in T37 and T38 jet aircraft. Tracking tests clearly distinguished between the nonflying group and all the flying groups. On the other hand, visual threshold tests did not distinguish between nonflying and flying groups except for grating contrast, which distinguished between the nonflying group and the pilot instructors. The sideways-motion tracking task was sensitive enough to distinguish between the various flying groups.