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Extraction of visual motion information for the control of eye and head movement during head-free pursuit.

Ackerley R, Barnes GR - Exp Brain Res (2011)

Bottom Line: We investigated how effectively briefly presented visual motion could be assimilated and used to track future target motion with head and eyes during target disappearance.Regression analysis revealed that the underlying compensatory response remained active, but with gain slightly less than unity (0.85), resulting in head-free gaze responses that were very similar to, but slightly greater than, head-fixed.The sampled velocity information was also used to grade head velocity, but in contrast to gaze, head velocity was similar whether the target was briefly or continuously presented, suggesting that head motion was controlled by internal mechanisms alone, without direct influence of visual feedback.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Life Sciences, University of Manchester, Moffat Building, Manchester, UK.

ABSTRACT
We investigated how effectively briefly presented visual motion could be assimilated and used to track future target motion with head and eyes during target disappearance. Without vision, continuation of eye and head movement is controlled by internal (extra-retinal) mechanisms, but head movement stimulates compensatory vestibulo-ocular reflex (VOR) responses that must be countermanded for gaze to remain in the direction of target motion. We used target exposures of 50-200 ms at the start of randomised step-ramp stimuli, followed by > 400 ms of target disappearance, to investigate the ability to sample target velocity and subsequently generate internally controlled responses. Subjects could appropriately grade gaze velocity to different target velocities without visual feedback, but responses were fully developed only when exposure was > 100 ms. Gaze velocities were sustained or even increased during target disappearance, especially when there was expectation of target reappearance, but they were always less than for controls, where the target was continuously visible. Gaze velocity remained in the direction of target motion throughout target extinction, implying that compensatory (VOR) responses were suppressed by internal drive mechanisms. Regression analysis revealed that the underlying compensatory response remained active, but with gain slightly less than unity (0.85), resulting in head-free gaze responses that were very similar to, but slightly greater than, head-fixed. The sampled velocity information was also used to grade head velocity, but in contrast to gaze, head velocity was similar whether the target was briefly or continuously presented, suggesting that head motion was controlled by internal mechanisms alone, without direct influence of visual feedback.

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Differences in response to target velocity. Left mid-ramp extinction responses; right short-ramp extinction responses. Examples of raw displacement responses for gaze (filled line), eye (dotted line) and head (dashed line) from subject 4 at a 10 deg/s and b 40 deg/s at PD = 150 ms. Average velocities for c gaze and d head over all subjects for each velocity at PD = 150 ms
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Fig2: Differences in response to target velocity. Left mid-ramp extinction responses; right short-ramp extinction responses. Examples of raw displacement responses for gaze (filled line), eye (dotted line) and head (dashed line) from subject 4 at a 10 deg/s and b 40 deg/s at PD = 150 ms. Average velocities for c gaze and d head over all subjects for each velocity at PD = 150 ms

Mentions: In the majority of trials, subjects were able to successfully determine the direction and speed of the target and initiate a pursuit response, even with only the briefest target presentation duration of 50 ms (Fig. 1a). The pursuit response was initiated after a latent period and exhibited the expected visually driven acceleration towards target velocity. Responses comprised both eye and rotational head movement to the MRE and SRE conditions. Eye displacement with respect to the head often exhibited nystagmus, presumably of vestibular origin, in which the smooth eye movement was in the opposite direction to the head (Fig. 1a, b). Virtually no anticipatory gaze movements were observed prior to target motion, as expected, given that target speed, direction and timing were randomised. Although the eyes and head worked in concert to produce the gaze response, gaze and head velocity had quite different trajectories and were differently affected by the initial presentation duration (compare mean gaze and head velocity traces in Fig. 1c, d). Following the initial visually driven component, subjects were able to sustain gaze responses that were scaled to target velocity (Fig. 2c) even though the response was frequently not initiated until the target had been extinguished.Fig. 1


Extraction of visual motion information for the control of eye and head movement during head-free pursuit.

Ackerley R, Barnes GR - Exp Brain Res (2011)

Differences in response to target velocity. Left mid-ramp extinction responses; right short-ramp extinction responses. Examples of raw displacement responses for gaze (filled line), eye (dotted line) and head (dashed line) from subject 4 at a 10 deg/s and b 40 deg/s at PD = 150 ms. Average velocities for c gaze and d head over all subjects for each velocity at PD = 150 ms
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3140921&req=5

Fig2: Differences in response to target velocity. Left mid-ramp extinction responses; right short-ramp extinction responses. Examples of raw displacement responses for gaze (filled line), eye (dotted line) and head (dashed line) from subject 4 at a 10 deg/s and b 40 deg/s at PD = 150 ms. Average velocities for c gaze and d head over all subjects for each velocity at PD = 150 ms
Mentions: In the majority of trials, subjects were able to successfully determine the direction and speed of the target and initiate a pursuit response, even with only the briefest target presentation duration of 50 ms (Fig. 1a). The pursuit response was initiated after a latent period and exhibited the expected visually driven acceleration towards target velocity. Responses comprised both eye and rotational head movement to the MRE and SRE conditions. Eye displacement with respect to the head often exhibited nystagmus, presumably of vestibular origin, in which the smooth eye movement was in the opposite direction to the head (Fig. 1a, b). Virtually no anticipatory gaze movements were observed prior to target motion, as expected, given that target speed, direction and timing were randomised. Although the eyes and head worked in concert to produce the gaze response, gaze and head velocity had quite different trajectories and were differently affected by the initial presentation duration (compare mean gaze and head velocity traces in Fig. 1c, d). Following the initial visually driven component, subjects were able to sustain gaze responses that were scaled to target velocity (Fig. 2c) even though the response was frequently not initiated until the target had been extinguished.Fig. 1

Bottom Line: We investigated how effectively briefly presented visual motion could be assimilated and used to track future target motion with head and eyes during target disappearance.Regression analysis revealed that the underlying compensatory response remained active, but with gain slightly less than unity (0.85), resulting in head-free gaze responses that were very similar to, but slightly greater than, head-fixed.The sampled velocity information was also used to grade head velocity, but in contrast to gaze, head velocity was similar whether the target was briefly or continuously presented, suggesting that head motion was controlled by internal mechanisms alone, without direct influence of visual feedback.

View Article: PubMed Central - PubMed

Affiliation: Faculty of Life Sciences, University of Manchester, Moffat Building, Manchester, UK.

ABSTRACT
We investigated how effectively briefly presented visual motion could be assimilated and used to track future target motion with head and eyes during target disappearance. Without vision, continuation of eye and head movement is controlled by internal (extra-retinal) mechanisms, but head movement stimulates compensatory vestibulo-ocular reflex (VOR) responses that must be countermanded for gaze to remain in the direction of target motion. We used target exposures of 50-200 ms at the start of randomised step-ramp stimuli, followed by > 400 ms of target disappearance, to investigate the ability to sample target velocity and subsequently generate internally controlled responses. Subjects could appropriately grade gaze velocity to different target velocities without visual feedback, but responses were fully developed only when exposure was > 100 ms. Gaze velocities were sustained or even increased during target disappearance, especially when there was expectation of target reappearance, but they were always less than for controls, where the target was continuously visible. Gaze velocity remained in the direction of target motion throughout target extinction, implying that compensatory (VOR) responses were suppressed by internal drive mechanisms. Regression analysis revealed that the underlying compensatory response remained active, but with gain slightly less than unity (0.85), resulting in head-free gaze responses that were very similar to, but slightly greater than, head-fixed. The sampled velocity information was also used to grade head velocity, but in contrast to gaze, head velocity was similar whether the target was briefly or continuously presented, suggesting that head motion was controlled by internal mechanisms alone, without direct influence of visual feedback.

Show MeSH
Related in: MedlinePlus