This paper addresses the question of how large the temporal delay between a visual and a haptic stimulus may be such that the stimuli are still perceived as being synchronous. Participants had to judge whether the moment at which a graphical object collided with a virtual wall occurred simultaneously with the moment at which a force was felt through a force feedback joystick. Participants either moved the joystick to drive the object (active touch) or held the joystick in a steady position while the object moved by itself (passive touch). Participants were found to be very sensitive to visual-haptic time delays. Sensitivity was higher for passive touch than for active touch. The minimum delay at which participants judged the stimuli as asynchronous was on average 45 ms. The delay at which the proportion of synchronous judgments reached a maximum was on average close to zero. The results indicate that the temporal accuracy of visual-haptic interfaces has to meet stringent requirements in order to optimize the overall realism that users experience. Actual or potential applications of this research include teleoperation, medical training, computer-aided-design, and scientific visualization.

To date, it is largely unknown which light settings define the optimum to steer alertness and cognitive control during regular daytime working hours. In the current article, we used a multimeasure approach combined with a relatively large sample size (N = 60) and a large range of intensity levels (20-2000 lux at eye level) to investigate the dose-dependent relationship between light and correlates of alertness and executive control during regular working hours in the morning and afternoon. Each participant was exposed to a single-intensity light level for 1 h after a 30-min baseline phase (100 lux at the eye) in the morning and afternoon (on separate days) during their daily routine. Results revealed no clear dose-dependent relationships between 1-h daytime light exposure and correlates of alertness or executive control. Subjective correlates showed only very modest linear relationships with the log-transformed illuminance, and we found no significant effects of light intensity on the behavioral and physiological indicators. Overall, these results suggest that daytime exposure to more intense light, at least for 1 h of exposure, may not systematically benefit alertness or executive functioning. However, future research is required to investigate effects of longer exposure durations and potential moderations by prior light exposure, personal characteristics, and spectrum.

Abstract. A haptic aftereffect of curved surfaces is demonstrated. Two spherical surfaces were presented sequentially to human subjects. They rested one hand on the first (conditioning) surface. After a fixed conditioning period they transferred their hand to the second (test) surface and judged whether the test surface was convex or concave. In experiment I the curvature of the conditioning surface was varied; the subject's judgment of convexity or concavity of the test surface was strongly shifted in the direction opposite to the curvature of the conditioning surface (negative aftereffect).Therefore, subjects judged a flat surface to be concave after being exposed to a convex surface. After a conditioning period of 5 s the shift was about 20% of the curvature of the conditioning surface.In experiment 2 the duration of the conditioning period was varied; the magnitude of the aftereffect could be described by a first-order integrator with a time constant of 2 s. In experiment 3 the time interval between the conditioning period and the touching of the second surface was varied; the magnitude of the aftereffect could be described by an exponential decay with a time constant of 40 s. It is concluded that the haptic aftereffect of curved surfaces is an important effect that occurs almost instantaneously and lasts for an appreciable period.

In haptics, the perceived (phenomenal) flatness of a surface is strongly influenced by a previous surface which has been statically touched. The mechanisms underlying this haptic aftereffect of curved surfaces are investigated. It is shown that the representation of curvature abstracted from the sense of touch, ie a high-level representation, is not affected during the aftereffect. This is concluded because: (1) the aftereffect does not exhibit intermanual transfer; (2) the way in which two successive surfaces are touched can influence the magnitude of the aftereffect; and (3) it is not necessary to touch a surface-active muscular contraction can also result in a shift of the phenomenal flatness. Furthermore, it is suggested that the physiological process involved in the aftereffect is a central process, ie it is located in the brain but it is distinct for each hemisphere. This is supported by the findings that: (1) the decay rate of the aftereffect is not influenced by the degree of peripheral stimulation during the decay; and (2) the aftereffect does not transfer from the adapted hand to the unadapted hand.

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