The need for speed: global optic flow speed influences steering

How do animals follow demarcated paths? Different species are sensitive to optic flow and one control solution is to maintain the balance of flow symmetry across visual fields; however, it is unclear whether animals are sensitive to changes in asymmetries when steering along curved paths. Flow asymmetries can alter the global properties of flow (i.e. flow speed) which may also influence steering control. We tested humans steering curved paths in a virtual environment. The scene was manipulated so that the ground plane to either side of the demarcated path produced larger or smaller asymmetries in optic flow. Independent of asymmetries and the locomotor speed, the scene properties were altered to produce either faster or slower globally averaged flow speeds. Results showed that rather than being influenced by changes in flow asymmetry, steering responded to global flow speed. We conclude that the human brain performs global averaging of flow speed from across the scene and uses this signal as an input for steering control. This finding is surprising since the demarcated path provided sufficient information to steer, whereas global flow speed (by itself) did not. To explain these findings, existing models of steering must be modified to include a new perceptual variable: namely global optic flow speed.

Corticospinal excitability during preparation for an anticipatory action is modulated by the availability of visual information

To intercept rapidly moving objects, people must predict the right time to initiate their actions. The timing of movement initiation in interceptions is thought to be determined when a perceptual variable specifying time to contact reaches a criterion value. If a response needs to be aborted, the performer must make a decision before this moment. It has been recently shown that the minimal time to suppress an anticipatory action takes longer during motion extrapolation than during continuous visual information. In experiment 1, we sought to determine whether or not the availability of visual information would 1) affect the latency to inhibit an anticipatory action, and 2) modulate the level of excitability in the motor cortex (M1). The behavioral results showed that the absence of visual information prolonged the latency to stop the movement as previously reported. The neurophysiological data indicated that corticospinal excitability levels were affected by the availability of visual information. In experiment 2, we sought to verify whether corticospinal excitability levels would also differ between the two visual conditions when the task did not involve response suppression. The results of experiment 2 indicated that excitability levels did not differ between visual conditions. Overall, our findings indicated that the buildup of motor activation can also play a role in determining different latencies to inhibit an anticipatory action. They also suggest that the buildup of motor activation in the corticospinal pathways can be strategically modulated to the requirements of the task during continuous visual information.

Space Flight: III. Isolation of Perceptual Variable in Parabola Flight Sickness with Countermeasure to Lower Gastric pH

Two factors of space sickness are discussed, one perceptual and the other physiological. Data from 2 adults on KC-135 airplane parabolic flights.

A Psychophysical Investigation of the Behavioural Relevance of Neurophysiological Feature Detectors (S Cells)

The aim of the study was to establish whether monaural auditory stimulation (a nonretinal perceptual variable) affects the class 1 oblique effect (a behavioural manifestation of simple cells). The left or right monaural stimulus was a pure tone, 1000 Hz, 70 dB(A), delivered continuously throughout the experimental session. The left or right monocular stimulus was a thin red phosphorescent bar the orientation of which was manipulated. In order to determine the oblique effect differential orientation thresholds for principal meridians were compared to those for oblique orientations. The results, indicating an interaction effect of the monaural and monocular stimulation on the magnitude of the oblique effect, are a further demonstration that the oblique effect is not as simple as some theories (derived from extrapolation from neurophysiological findings) would imply.

Cognitive Complexity and the Perception of Attitude Objects: An Examination of Halo Error

The purpose of this study was to examine the relationship between cognitive complexity, a structural variable of cognition, and halo error, a perceptual variable. Data were obtained from 99 subjects who evaluated eight brands of toothpaste and 10 makes of automobiles along with a Bieri Reptest for each product category. As predicted, complexity was significantly and inversely related to the variation in belief ratings (halo) for each brand of toothpaste or make of automobile.