Limits...
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.

Show MeSH

Related in: MedlinePlus

a and b show averaged gaze, head and eye-in-head velocity trajectories in MRE and SRE conditions, respectively. Dashed magenta and red traces indicate best-fit predictions of head-free eye-in-head and gaze velocity, respectively. Green dashed trace indicates eye velocity difference between head-free and head-fixed eye-in-head responses. Black vertical arrow indicates end of extinction. Colour coding of traces is given in legend. Best-fit functions obtained by regression analysis of head-free gaze velocity versus the combination of head velocity and head-fixed eye velocity. c and d show the eye velocity difference signal plotted point-by-point against head velocity for MRE and SRE conditions, respectively. Data from each PD condition plotted in separate colour as shown in legend. Dashed black line indicates the ideal compensatory gain of −1
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3140921&req=5

Fig5: a and b show averaged gaze, head and eye-in-head velocity trajectories in MRE and SRE conditions, respectively. Dashed magenta and red traces indicate best-fit predictions of head-free eye-in-head and gaze velocity, respectively. Green dashed trace indicates eye velocity difference between head-free and head-fixed eye-in-head responses. Black vertical arrow indicates end of extinction. Colour coding of traces is given in legend. Best-fit functions obtained by regression analysis of head-free gaze velocity versus the combination of head velocity and head-fixed eye velocity. c and d show the eye velocity difference signal plotted point-by-point against head velocity for MRE and SRE conditions, respectively. Data from each PD condition plotted in separate colour as shown in legend. Dashed black line indicates the ideal compensatory gain of −1

Mentions: In the head-free condition, head rotation would be expected to evoke a compensatory VOR response and consistent with this, eye-in-head position often moved in the opposite direction to the head (see examples in Fig. 2a, b). On average, eye-in-head velocity was of opposite polarity to head velocity towards the end of extinction, as shown in Fig. 5 (cyan trace). If it is assumed that the internal drive that gives rise to the sustained response in the head-fixed condition is identical in head-fixed and head-free conditions, the compensatory (VOR) response should be revealed by calculating an eye velocity difference signal, i.e. the difference between head-free eye-in-head velocity and head-fixed eye velocity. This approach is similar to that used by Lefevre et al. (1992) when investigating compensatory response characteristics during saccadic gaze shifts. As indicated in Fig. 5, the eye velocity difference signal (black dashed trace) clearly has a similar trajectory to head velocity, but is of opposite polarity. It normally appeared slightly delayed with respect to head velocity. Plotting the difference signal versus head velocity point-by-point over the first 650 ms (i.e. prior to target reappearance in any condition) revealed an apparently linear relationship in all subjects (Fig. 5c, d), with a clear overlay of responses to different PD values.Fig. 5


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)

a and b show averaged gaze, head and eye-in-head velocity trajectories in MRE and SRE conditions, respectively. Dashed magenta and red traces indicate best-fit predictions of head-free eye-in-head and gaze velocity, respectively. Green dashed trace indicates eye velocity difference between head-free and head-fixed eye-in-head responses. Black vertical arrow indicates end of extinction. Colour coding of traces is given in legend. Best-fit functions obtained by regression analysis of head-free gaze velocity versus the combination of head velocity and head-fixed eye velocity. c and d show the eye velocity difference signal plotted point-by-point against head velocity for MRE and SRE conditions, respectively. Data from each PD condition plotted in separate colour as shown in legend. Dashed black line indicates the ideal compensatory gain of −1
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3140921&req=5

Fig5: a and b show averaged gaze, head and eye-in-head velocity trajectories in MRE and SRE conditions, respectively. Dashed magenta and red traces indicate best-fit predictions of head-free eye-in-head and gaze velocity, respectively. Green dashed trace indicates eye velocity difference between head-free and head-fixed eye-in-head responses. Black vertical arrow indicates end of extinction. Colour coding of traces is given in legend. Best-fit functions obtained by regression analysis of head-free gaze velocity versus the combination of head velocity and head-fixed eye velocity. c and d show the eye velocity difference signal plotted point-by-point against head velocity for MRE and SRE conditions, respectively. Data from each PD condition plotted in separate colour as shown in legend. Dashed black line indicates the ideal compensatory gain of −1
Mentions: In the head-free condition, head rotation would be expected to evoke a compensatory VOR response and consistent with this, eye-in-head position often moved in the opposite direction to the head (see examples in Fig. 2a, b). On average, eye-in-head velocity was of opposite polarity to head velocity towards the end of extinction, as shown in Fig. 5 (cyan trace). If it is assumed that the internal drive that gives rise to the sustained response in the head-fixed condition is identical in head-fixed and head-free conditions, the compensatory (VOR) response should be revealed by calculating an eye velocity difference signal, i.e. the difference between head-free eye-in-head velocity and head-fixed eye velocity. This approach is similar to that used by Lefevre et al. (1992) when investigating compensatory response characteristics during saccadic gaze shifts. As indicated in Fig. 5, the eye velocity difference signal (black dashed trace) clearly has a similar trajectory to head velocity, but is of opposite polarity. It normally appeared slightly delayed with respect to head velocity. Plotting the difference signal versus head velocity point-by-point over the first 650 ms (i.e. prior to target reappearance in any condition) revealed an apparently linear relationship in all subjects (Fig. 5c, d), with a clear overlay of responses to different PD values.Fig. 5

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