Biomedical subjects

Nick Fogt

Publications and source records attributed to Nick Fogt.

5 recordsLinked to original sources

PubMed2005

Saccadic latencies for achromatic and chromatic targets.

The purpose of this experiment was to compare saccadic latencies for supra-threshold achromatic and chromatic targets of equivalent contrast. Two experiments were performed. In the first experiment, subjects made saccades to horizontal and vertical chromatic (red, green, and blue) targets. The luminance of these targets was matched to the luminance of the white background. In the second experiment, subjects made saccades to horizontal and vertical achromatic targets whose luminance contrast was matched to the chromatic contrast of the targets in the first experiment using the CIE L*a*b* color space. In the first experiment, the saccadic latencies did not vary significantly (p = 0.074) for the different target colors. However, in the second experiment the mean latency for achromatic targets (268.6 ms +/- 53.1) varied significantly from the pooled latency for color targets (318.4 ms +/- 75.1).

Adult↗

PubMed2005

Fixational errors for two-dimensional tracking tasks with black and complex backgrounds.

INTRODUCTION: In low-level flight, pilots must track objects against an array of background objects. The purpose of this study was to determine what influence the objects in a flight simulator background have on catch-up saccades and overall fixational errors during head-free ocular tracking. METHODS: Two experiments were performed. In Experiment 1, subjects tracked a two-dimensional target consisting of the sum of five sinusoids (frequencies 0.30-1.25 Hz) horizontally and six sinusoids (frequencies 0.24-1.25 Hz) vertically in three background conditions. In one condition, the background was black, in another condition the projected background was the Microsoft screensaver "Starfield Simulation," and in another condition the background was that seen from a helicopter during a flight recorded in the Microsoft 2000 Flight Simulator software. Experiment 2 was the same as Experiment 1, except the frequency of each target sinusoid was doubled. RESULTS: Radial fixational errors were calculated. In Experiment 1, the mean errors were 3.73 +/- 0.57 degrees (black background), 3.75 +/- 0.57 degrees (starfield simulation), and 3.87 +/- 0.70 degrees (flight simulator). These values were not significantly different. In Experiment 2, the mean errors were 7.04 +/- 0.54degrees (black background), 7.04 +/- 0.38 degrees (starfield simulation), and 8.15 +/- 0.96 degrees (flight simulator). These values were significantly different. DISCUSSION: The distractors of the starfield simulation and flight simulator background did not influence catch-up saccades (Experiment 1). In Experiment 2, the flight simulator background increased the mean fixational errors most likely by drawing attention from the target.

Adult↗

PubMed2004

Magnetic field coil measurements of the accuracy of extreme gaze ocular fixation.

PURPOSE: (1) To assess the adequacy of the magnetic field coil method (MFCM) for measures of extreme gaze ocular fixation; and (2) to measure the accuracy of ocular fixation for a short duration at gaze angles of 10 to 40 degrees. METHODS: Seven subjects participated. Two experiments were performed on the same day. In both experiments, the head and eye were rotated in opposite directions. In the first experiment, search coil slippage was assessed using photographs of a scleral search coil worn on one eye. These photographs were taken with a slitlamp biomicroscope equipped with a digital photography system as subjects rotated the eyes through nasal angles up to 40 degrees. In the second experiment, measures of ocular position were made using the MFCM as the eye was rotated through nasal angles up to 40 degrees to fixate a light-emitting diode target under two conditions. In one condition, subjects simply aimed the eye at the target. In the other, subjects placed a foveal afterimage on the target as the target was viewed through a pinhole. RESULTS: Temporal search coil slippage >10 arc min was noted for three subjects. For one subject, this slippage occurred at gaze angles > or =20 degrees, whereas for the other subjects, the slippage appeared at gaze angles of > or =30 degrees. Ocular fixation had to be assessed from the differences in fixation position between the two conditions in the second experiment because of search coil slippage and because the relationship between the anterior and posterior portions of the eyes changed for some individuals as the gaze angle changed. Fixation was usually accurate (within 10 arc min). There were occasional instances where fixation errors >15 arc min occurred, but we believe that all but one of these cases were attributable to poor localization of the afterimage. CONCLUSION.: Scleral search coils can slip on some individuals in extreme gaze. Search coils may also be inadequate to indicate the direction of the fovea in extreme gaze for some individuals because the relationship between the anterior and posterior portions can change with gaze angle. Once artifacts associated with the MFCM and localization of the afterimage are accounted for, ocular fixation is almost always within 10 arc min of the fixation target at gaze angles of 10 to 40 degrees.

Adult↗

PubMed2002

Ocular fixation during eye and head tracking with and without a visual cue to head position.

PURPOSE: This experiment had two purposes. The first purpose was to compare ocular fixation during eye tracking, head tracking, and head tracking with a visual cue to head position. The second purpose was to compare head tracking with and without a visual cue to head position. METHODS: Eleven subjects tracked a pseudo-random laser target in three conditions. In one condition (Condition 1), subjects tracked the target primarily with the eyes. In a second condition (Condition HT), subjects tracked the target with the head but no visual cue to head position was provided. In the final condition, subjects tracked the target with the head and were given a visual cue to head position (Condition HR). RESULTS: On average, ocular fixation was worst in Condition HR and similar in Condition 1 and Condition HT. Mismatches in target and head velocity greater than 60 degrees x sec(-1) occurred more frequently in Condition HR than in Condition HT. CONCLUSIONS: Ocular tracking of a pseudo-random target is adversely affected in a minor way by head movement, but tracking declines significantly when head tracking is performed with a visual cue to head position. In terms of velocity matching, head tracking is also adversely affected by a head position cue.

Adult↗

PubMed2002

The influence of head movement on the accuracy of a rapid pointing task.

BACKGROUND: Eye-hand coordination contributes to sports performance. The positive effect of head movement on the accuracy of eye-hand coordination of some subjects has been demonstrated for self-paced or single tasks, but not for rapid, repetititive tasks, such as those sometimes required in sports. The purpose of this study was to determine whether head movement is detrimental to performance of a rapid, repetitive pointing task. METHODS: Pointing accuracy and speed were tested using the AcuVision 1000 trainer, a device designed to assess and train eye-hand coordination. Twenty-six subjects participated. In one trial, subjects were told to turn their heads toward the targets as they pointed at them. In a second trial, subjects were told to keep their heads stationary as they pointed at the targets. The order of the trials was counter-balanced and subjects were randomly assigned to one of the orders. RESULTS: Pointing accuracy was significantly greater in the head movement trial than in the no head movement trial. CONCLUSIONS: Head movement increased the accuracy of this rapid task. Head movement probably allows more-accurate encoding of target position by maintaining the eyes in less-eccentric positions of gaze.

Adolescent↗