Biomedical subjects

Heiko Hecht

Publications and source records attributed to Heiko Hecht.

9 recordsLinked to original sources

PubMed2005

Naive optics: acting on mirror reflections.

It is known that naive observers have striking misconceptions about mirror reflections. In 5 experiments, this article systematically extends the findings to graphic stimuli, to interactive visual tasks, and finally to tasks involving real mirrors. The results show that the perceptual knowledge of nonexpert adults is far superior to their conceptual knowledge. Whereas conceptual errors include the assumption of left-right reversals in mirror images and often blatant extensions of the boundary of mirror space, the perceptual context prevents most such errors. However, a consistent bias to misjudge objects in mirrors too far to the outside is demonstrable in all cases including tasks with real mirrors. The authors present a 2-stage hypothesis consisting of an implicit bias of judging the mirror surface to be turned toward the observer's line of sight followed by a normalization that becomes explicit.

Adult↗

PubMed2005

Boundary extension: the role of magnification, object size, context, and binocular information.

Boundary extension is a tendency to remember close-up scenes as if they extended beyond the occluding boundaries. The authors explored the contributing factors using brief retention intervals and computer-generated images. Boundary extension turns out to be more complex than previously thought and is not linked to the effects of image magnification and field-of-view changes. Although this is consistent with the idea that boundary extension is the product of the activation of a mental schema that provides information of what is likely to exist outside the picture boundaries, the authors also found that properties of the object at the center of the picture can affect boundary extension independently of the information at the boundaries. In a test of boundary extension using stereograms, the effect does not seem to depend on amount of perceived depth, suggesting a weaker link to perception of space than previously hypothesized.

Environment↗

PubMed2003

Naive optics: Predicting and perceiving reflections in mirrors.

Undergraduate students predicted what would be made visible by a planar mirror. A paper-and-pencil task confirmed previous findings that when approaching a mirror from the side, participants expected to see their reflection in the mirror earlier than they actually would. This early response was found for all mirrors when the observer moved horizontally--even when the mirror was placed on the floor or the ceiling--but not when the observer moved vertically (in a lift). The data support the hypothesis that many people imagine the world in the mirror as rotated around the vertical axis. When participants had to judge manipulated mirror reflections according to their naturalness, a high degree of tolerance was found. In contrast to the prediction task, a rotation around the vertical axis was judged to be less natural than other distortions. The authors conclude that perceptual knowledge and predictive knowledge lead to different patterns of errors. ((c) 2003 APA, all rights reserved)

Adult↗

PubMed2003

Adaptation of the vestibulo-ocular reflex, subjective tilt, and motion sickness to head movements during short-radius centrifugation.

Head movements made while the whole body is rotating at unusually high angular velocities (here with supine body position about an earth-vertical axis) result in inappropriate eye movements, sensory illusions, disorientation, and frequently motion sickness. We investigated the acquisition and retention of sensory adaptation to cross-coupled components of the vestibulo-ocular reflex (VOR) by asking eight subjects to make headturns while being rotated at 23 rpm on two consecutive days, and again a week later. The dependent measures were inappropriate vertical VOR, subjective tilt, and motion sickness in response to 90 degrees yaw out-of-plane head movements. Motion sickness was evaluated during and following exposure to rotation. Significant adaptation effects were found for the slow phase velocity of vertical nystagmus, the reported magnitude of the subjective tilt experienced during head turns, and motion-sickness scores. Retention of adaptation over a six-day rest period without rotation occurred, but was not complete for all measures. Adaptation of VOR was fully maintained while subjective tilt was only partially maintained and motion-sickness scores continued to decrease. Practical implications of these findings are discussed with particular emphasis on artificial gravity, which could be produced in weightlessness by means of a short-radius (2 m) rotator.

Adaptation, Physiological↗

PubMed2002

Naive optics: understanding the geometry of mirror reflections.

Paper-and-pencil tasks showed that many university students believed that when laterally approaching a mirror, they would see a reflection in the mirror before it was geometrically possible. Participants failed to adequately factor in the observer's location in the room. However, when asked about the behavior of a ray of light, participants knew about the law of reflection. No differences between psychology and physics students were detected, suggesting that the phenomenon is widespread and refractory to training. The findings were replicated with observers making judgments about image locations in a real room using a pretend mirror. Possible heuristics about mirror reflection that might explain the data are discussed. Naive optics is a promising venue to further knowledge of how observers understand basic laws of physics.

Adolescent↗

PubMed2002

The impact of spatiotemporal sampling on time-to-contact judgments.

When motion in the frontoparallel plane is temporally sampled, it is often perceived to be slower than its continuous counterpart. This finding stands in contrast to humans' ability to extrapolate and anticipate constant-velocity motion. We investigated whether this sampling bias generalizes to motion in the sagittal plane (i.e., objects approaching the observer). We employed a paradigm in which observers judged the arrival time of an oncoming object. We found detrimental effects of time sampling on both perceived time to contact and time to passage. Observers systematically overestimated the time it would take a frontally approaching object to intersect their eye plane. To rule out artifacts inherent in computer simulation, we replicated the experiment, using real objects. The bias persisted and proved to be robust across a large range of temporal and spatial variations. Energy and pooling mechanisms are discussed in an attempt to understand the effect.

Adult↗

PubMed2002

Adapting to artificial gravity (AG) at high rotational speeds.

Short-radius centrifugation offers a promising countermeasure to the adverse effects of prolonged weightlessness. Head movements made in a rotating environment elicit Coriolis effects, which seriously compromise sensory and motor processes. We have previously found that, contrary to common belief, participants can adapt to the Coriolis effects associated with single-quadrant yaw head turns during 23-rpm short-radius centrifugation, while maintaining their adaptation to stationary environments. Here, we focus on motion sickness and illusory motion, the most problematic subjective side effects. We present encouraging data that such context-specific adaptation generalizes immediately to a different centrifuge environment. It also generalizes quickly to Coriolis forces in the opposite direction. Implications for AG implementation are discussed.

NASA Discipline Neuroscience↗

PubMedDate not supplied

Artificial gravity--head movements during short-radius centrifugation: influence of cognitive effects.

Short-radius centrifugation is a potential countermeasure against the effects of prolonged weightlessness. Head movements in a rotating environment, however, induce serious side effects: inappropriate vestibular ocular reflexes (VOR), body-tilt illusions and motion sickness induced by cross-coupled accelerations on a rotating platform. These are well predicted by a semicircular canal model. The present study investigates cognitive effects on the inappropriate VOR and the illusory sensations experienced by subjects rotating on a short-radius centrifuge (SRC). Subjects (N=19) were placed supine on a rotating horizontal bed with their head at the center of rotation. To investigate the extent to which they could control their sensations voluntarily, subjects were asked alternatively to "fight" (i.e. to try to resist and suppress) those sensations, or to "go" with (i.e. try to enhance or, at least, acquiesce in) them. The only significant effect on the VOR of this cognitive intervention was to diminish the time constant characterizing the decay of the nystagmus in subjects who had performed the "go" (rather than the "fight") trials. However, illusory sensations, as measured by reported subjective intensities, were significantly less intense during the "fight" than during the "go" trials. These measurements also verified an asymmetry in illusory sensation known from earlier experiments: the illusory sensations are greater when the head is rotated from right ear down (RED) to nose up (NU) posture than from NU to RED. The subjects habituated, modestly, to the rotation between their first and second sequences of trials, but showed no better (or worse) suppression of illusory sensations thereafter. No significant difference in habituation was observed between the "fight" and "go" trials.

Adaptation, Physiological↗

PubMedDate not supplied

Sensorimotor aspects of high-speed artificial gravity: I. Sensory conflict in vestibular adaptation.

Short-radius centrifugation offers a promising and affordable countermeasure to the adverse effects of prolonged weightlessness. However, head movements made in a fast rotating environment elicit Coriolis effects, which seriously compromise sensory and motor processes. We found that participants can adapt to these Coriolis effects when exposed intermittently to high rotation rates and, at the same time, can maintain their perceptual-motor coordination in stationary environments. In this paper, we explore the role of inter-sensory conflict in this adaptation process. Different measures (vertical nystagmus, illusory body tilt, motion sickness) react differently to visual-vestibular conflict and adapt differently. In particular, proprioceptive-vestibular conflict sufficed to adapt subjective parameters and the time constant of nystagmus decay, while retinal slip was required for VOR gain adaptation. A simple correlation between the strength of intersensory conflict and the efficacy of adaptation fails to explain the data. Implications of these findings, which differ from existing data for low rotation rates, are discussed.

Adaptation, Physiological↗