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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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Related in: MedlinePlus

Examples of velocity profiles for both head-free and head-fixed pursuit in the mid-ramp extinction (MRE) and short-ramp extinction (SRE) conditions. Responses are averaged across 6 subjects and 4 repeats/subject for PD = 150 ms and target velocity 10 deg/s (a) and 20 deg/s (b). Black vertical arrow indicates end of extinction in MRE condition
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Fig4: Examples of velocity profiles for both head-free and head-fixed pursuit in the mid-ramp extinction (MRE) and short-ramp extinction (SRE) conditions. Responses are averaged across 6 subjects and 4 repeats/subject for PD = 150 ms and target velocity 10 deg/s (a) and 20 deg/s (b). Black vertical arrow indicates end of extinction in MRE condition

Mentions: The head-free results from the present experiment were compared with the results from matched subjects in the head-fixed paradigm (from Barnes and Collins 2008b; head-fixed eye displacement and velocity now referred to as gaze displacement and velocity, respectively, for comparison). Responses made to target velocity levels of 10 and 20 deg/s for Controls and all presentation durations were compared. Figure 4a, b show gaze velocity trajectories for head-fixed and head-free responses in the MRE and SRE conditions at 10 and 20 deg/s, respectively. Three distinct trends are revealed in Fig. 4: (1) head-free responses for both MRE and SRE conditions had higher gaze velocity than head-fixed responses; (2) the differences between the head-fixed and the head-free SRE responses were larger than those for the MRE responses; (3) the increase in target velocity from 10 to 20 deg/s induced a proportional increase in gaze velocity in both the head-fixed and the head-free responses; and (4) the initial part of the gaze velocity response was very similar in head-fixed and head-free conditions, but with head free, gaze velocity continued for longer and reached a higher level that was sustained throughout extinction.Fig. 4


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)

Examples of velocity profiles for both head-free and head-fixed pursuit in the mid-ramp extinction (MRE) and short-ramp extinction (SRE) conditions. Responses are averaged across 6 subjects and 4 repeats/subject for PD = 150 ms and target velocity 10 deg/s (a) and 20 deg/s (b). Black vertical arrow indicates end of extinction in MRE condition
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3140921&req=5

Fig4: Examples of velocity profiles for both head-free and head-fixed pursuit in the mid-ramp extinction (MRE) and short-ramp extinction (SRE) conditions. Responses are averaged across 6 subjects and 4 repeats/subject for PD = 150 ms and target velocity 10 deg/s (a) and 20 deg/s (b). Black vertical arrow indicates end of extinction in MRE condition
Mentions: The head-free results from the present experiment were compared with the results from matched subjects in the head-fixed paradigm (from Barnes and Collins 2008b; head-fixed eye displacement and velocity now referred to as gaze displacement and velocity, respectively, for comparison). Responses made to target velocity levels of 10 and 20 deg/s for Controls and all presentation durations were compared. Figure 4a, b show gaze velocity trajectories for head-fixed and head-free responses in the MRE and SRE conditions at 10 and 20 deg/s, respectively. Three distinct trends are revealed in Fig. 4: (1) head-free responses for both MRE and SRE conditions had higher gaze velocity than head-fixed responses; (2) the differences between the head-fixed and the head-free SRE responses were larger than those for the MRE responses; (3) the increase in target velocity from 10 to 20 deg/s induced a proportional increase in gaze velocity in both the head-fixed and the head-free responses; and (4) the initial part of the gaze velocity response was very similar in head-fixed and head-free conditions, but with head free, gaze velocity continued for longer and reached a higher level that was sustained throughout extinction.Fig. 4

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