Dorion B. Liston

Effects of Prior Information and Reward on Oculomotor and Perceptual Choices

Expectations about the environment influence motor behavior. In simple tasks, for example, prior knowledge about which stimulus event will likely occur or which response will likely be rewarded induces a tendency to take the favored action (i.e., a motor or response bias), especially when sensory information is sparse or ambiguous. Models of choice behavior account for this bias by weighting decision alternatives unequally, either at an early sensory-input stage or at a downstream motor-output stage. These two alternatives can be distinguished empirically; the former predicts an altered percept that correlates with motor bias, the latter predicts no perceptual effect. By varying the prior probability of target or reward location, we induced biased oculomotor responses in a brightness selection task with human subjects. We found that the induced motor bias was correlated with an amplification of both the sensory signals and internal noise underlying brightness perception, without a systematic change in perceived overall brightness. We also found that the magnitude of the sensory amplification was correlated with the amount of noise in the brightness percept, consistent with a multiplicative weighting factor located downstream from the limiting internal sensory noise. Our data demonstrate that prior knowledge (about target location or reward) shapes visual signals for perception and action in parallel but does not improve the quality (i.e., signal-to-noise ratio) of sensory processing.

Visual Features Involving Motion Seen from Airport Control Towers

Visual motion cues are used by tower controllers to support both visual and anticipated separation. Some of these cues are tabulated as part of the overall set of visual features used in towers to separate aircraft. An initial analyses of one motion cue, landing deceleration, is provided as a basis for evaluating how controllers detect and use it for spacing aircraft on or near the surface. Understanding cues like it will help determine if they can be safely used in a remote/virtual tower in which their presentation may be visually degraded.

Oculometric Assessment of Sensorimotor Impairment Associated with TBI.

Supplemental digital content is available in the text.

Onset of positional vertigo during exposure to combined G loading and chest-to-spine vibration.

BACKGROUND Aerospace environments commonly expose pilots to vibration and sustained acceleration, alone and in combination. CASE REPORTS Of 16 experimental research participants, 3 reported symptoms of vertigo and signs of torsional nystagmus during or shortly following exposure to sustained chest-to-spine (+3.8 Gx) acceleration (G loading) and chest-to-spine (0.5 g(x)) vibration in the 8-16 Hz band. Two of the participants reported intermittent vertigo for up to 2 wk, were diagnosed with benign paroxysmal positional vertigo (BPPV), and were treated successfully with the Epley Maneuver. On a follow-up survey, a third participant reported transient BPPV-like vertigo, which resolved spontaneously. The follow-up survey also prompted participants to self-report other effects following research protocol exposure to vibration and G loading, revealing details about other minor and transient, but more common, effects that resolved within 3 h. DISCUSSION Our studies indicated a significantly elevated incidence of BPPV following exposure to vibration plus G loading compared to vibration alone that was positively correlated with participant age. One mechanism for the rolling sensation in BPPV involves broken or dislodged otoconia floating within one of the posterior semicircular canals, making the canal gravity-sensitive. Our observations highlight a heretofore unforeseen risk of otolith damage sustained during launch, undetectable in space, potentially contributing to vertigo and perceived tumbling upon re-entry from microgravity.

Design and validation of a simple eye-tracking system

To address the need for portable systems to collect high-quality eye movement data for field studies, this paper shows how one might design, test, and validate the spatiotemporal fidelity of a homebrewed eye-tracking system. To assess spatial and temporal precision, we describe three validation tests that quantify the spatial resolution and temporal synchronization of data acquisition. First, because measurement of pursuit eye movements requires a visual motion display, we measured the timing of luminance transitions of several candidate LCD monitors so as to ensure sufficient stimulus fidelity. Second, we measured eye position as human observers (n=20) ran a nine-point calibration in a clinical-grade chin rest, delivering eye-position noise of 0.22 deg (range: 0.09-0.29 deg) and accuracy of 0.97 deg (range: 0.54-1.89 deg). Third, we measured the overall processing delay in the system to be 5.6 ms, accounted for by the response dynamics of our monitor and the duration of one camera frame. The validation methods presented can be used: 1) to ensure that eye-position accuracy and precision are sufficient to support scientific and clinical studies and are not limited by the hardware or software, and 2) the eyetracker, display, and experiment-control software are effectively synchronized.

G-loading and vibration effects on heart and respiration rates.

BACKGROUND Operational environments expose pilots and astronauts to sustained acceleration (G loading) and whole-body vibration, alone and in combination. Separately, the physiological effects of G loading and vibration have been well studied; both have effects similar to mild exercise. The few studies of combined G loading and vibration have not reported an interaction between these factors on physiological responses. METHODS We tested the effects of G loading (+1 and +3.8 G(x)) and vibration (0.5 gx at 8, 12, and 16 Hz), alone and in combination, on heart and respiration rate. RESULTS We observed an effect of G loading on heart rate (average increase of 23 bpm, SD 12) and respiration rate (average increase of 5 breaths per minute, SD 5), an effect of vibration on heart rate, and an interaction on heart rate. With vibration, we observed heart rate increases of 4 bpm (SD: 3) with no increase in respiration rate. In the +1 G(x) condition, the largest heart rate increase occurred during low-frequency (8 Hz) vibration, while at +3.8 G(x), the largest heart rate increase occurred during high-frequency (16 Hz) vibration, demonstrating interaction. DISCUSSION Consistent with previous reports, our G-loading and vibration effects are similar to mild exercise. In addition, we observed an interaction between G loading and vibration on heart rate, with maximum heart rates occurring at a higher vibration frequency at +3.8 G(x) compared to +1 G(x). The observed interaction demonstrates that G-loading and vibration effects are not independent and can only be properly assessed during combined exposure.