Visual control of steering in curve driving.

This pair of studies investigated steering in the absence of continuous visual information. In a driving simulator, participants steered a curving path that was displayed either continuously or intermittently. Optic flow conditions were manipulated to alter the nature of the heading information with respect to the path being steered. Removing or biasing heading information had little effect on steering even during long and frequent path occlusions as long as turn rate was available. This demonstrates that participants can use intermittent views of the path to plan their steering actions and optic flow to accurately update vehicle turns with respect to that path.

Incomplete recovery of cerebral blood flow dynamics in sufficiently treated high blood pressure.

OBJECTIVE: Whether cerebrovascular regulation is different in patients with controlled high blood pressure (HBP) with and without small vessel disease (SVD). METHODS: Sixty-seven healthy controls (mean age ±â€ŠSD, 45 ±â€Š16 years; 30 women, 37 men) and 40 patients (mean age, 64 ±â€Š13 years; 14 women, 26 men) with HBP and different stages of SVD, underwent simultaneous recordings of the spontaneous fluctuations of BP, blood flow velocity (CBFV) in both middle cerebral arteries (MCA), and of end-tidal CO2 (ETCO2). Coherence and transfer function gain and phase between BP and CBFV were assessed in the frequency ranges of VLF (0.02-0.07 Hz), low frequency (0.07-0.15), and high frequency (>0.15). BP SD indicated BP variability (BPV). RESULTS: In controls (BP, 86 ±â€Š13 mmHg; ETCO2, 39 ±â€Š4 mmHg; BPV, 15 ±â€Š6 mmHg), gain, phase and coherence were not age-dependent in simple or a multiple regression models. BPV correlated significantly in both MCAs with gain in low frequency and high frequency, and with phase in VLF and high frequency. In patients (BP, 91 ±â€Š16 mmHg, ETCO2, 39 ±â€Š4 mmHg, BPV 18 ±â€Š5 mmHg), only gain showed some differences between different SVD groups. Comparing all patients with 25 controls of similar age and sex, patients exhibited significantly (P < 0.05-P < 0.005): increased coherence and gain in VLF, decreased phase in VLF and low frequency, correlations between BPV with phase in low frequency (left) and with gain in VLF (left) and in high frequency (left and right). CONCLUSION: Phase seems an age independent autoregulatory index. In controlled HBP, CBF regulation is degraded at longlasting CBF changes; BPV effects lose their physiological bilateral distribution.

Changing lanes: inertial cues and explicit path information facilitate steering performance when visual feedback is removed.

Can driver steering behaviors, such as a lane change, be executed without visual feedback? In a recent study with a fixed-base driving simulator, drivers failed to execute the return phase of a lane change when steering without vision, resulting in systematic final heading errors biased in the direction of the lane change. Here we challenge the generality of that finding. Suppose that, when asked to perform a lane (position) change, drivers fail to recognize that a heading change is required to make a lateral position change. However, given an explicit path, the necessary heading changes become apparent. Here we demonstrate that when heading requirements are made explicit, drivers appropriately implement the return phase. More importantly, by using an electric vehicle outfitted with a portable virtual reality system, we also show that valid inertial information (i.e., vestibular and somatosensory cues) enables accurate steering behavior when vision is absent. Thus, the failure to properly execute a lane change in a driving simulator without a moving base does not present a fundamental problem for feed-forward driving behavior.

Visual control of action without retinal optic flow.

In everyday life, the optic flow associated with the performance of complex actions, like walking through a field of obstacles and catching a ball, entails retinal flow with motion energy (first-order motion). We report the results of four complex action tasks performed in virtual environments without any retinal motion energy. Specifically, we used dynamic random-dot stereograms with single-frame lifetimes (cyclopean stimuli) such that in neither eye was there retinal motion energy or other monocular information about the actions being performed. Performance on the four tasks with the cyclopean stimuli was comparable to performance with luminance stimuli, which do provide retinal optic flow. The near equivalence of the two types of stimuli indicates that if optic flow is involved in the control of action, it is not tied to first-order retinal motion.