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J N Vickers

Publications and source records attributed to J N Vickers.

4 recordsLinked to original sources
PubMed1997

Where and when do we look as we approach and step over an obstacle in the travel path?

Spatio-temporal gaze behaviour patterns were analysed as normal participants wearing a mobile eye tracker approached and stepped over obstacles of varying height in the travel path. We examined the frequency and duration of three types of gaze fixation with respect to the participants' stepping patterns: obstacle fixation (ObsFix); travel fixation (TravFix) (when the gaze is stable and travelling at the speed of whole body) and fixation in the 4-6m region (Fix4-6). During the approach phase to the obstacle, participants fixated on the obstacle for approximately 20% of the travel time. Only Fix4-6 duration was modulated as a function of obstacle height by regulating the frequency and reflected the increased time needed for detection of the small low contrast obstacle in the travel path. Frequency of ObsFix increased significantly as a function of obstacle height and reflected visuo-motor transformation needed for limb elevation control. Participants did not fixate on the obstacle as they were stepping over, but did the planning in the steps before. TravFix duration and frequency was constant while Fix4-6 duration was higher in the step before and step over the obstacle reflecting visual search of the landing area for the lead limb following obstacle avoidance. These results clearly show that obstacle information provided by vision is used in a feed-forward rather than on-line control mode to regulate locomotion. Information about self-motion acquired from optic flow during TravFix can be used to control velocity of locomotion.

Fixation, Ocular↗
PubMed1996

Visual control when aiming at a far target.

Gaze behavior of elite basketball athletes was determined as they performed 10 accurate and 10 inaccurate free throws (FTs) to a regulation basket wearing an eye tracker that permitted normal accuracy. Experts (mean FT = 78%) differed significantly from near experts (mean FT = 56%) in having a longer fixation on the target combined with an earlier fixation offset during the shooting action. These results, which depart from current models of near aiming, are tentatively explained using a location-suppression hypothesis. During the early phases of the aiming action, a fixation of long duration is needed on a specific target location. As the aiming action is then performed, vision appears to be a liability and is suppressed.

Adolescent↗
PubMed1992

Gaze control in putting.

The gaze of low and higher handicap golfers was assessed while they performed consecutive putts from 3 m, wearing an eye-movement helmet that permitted normal mobility. MANOVA (count and duration), with univariate follow-up, revealed significant differences in gaze between five low (LH, 0-8) and seven higher handicap golfers (HH, 10-16). The LH (ie more highly skilled) golfers were found to use a variable form of gaze control in which longer fixation durations on the ball and target were observed, and there were fewer fixations on the club and surface, with more express saccades and quicker saccades between gaze locations. The HH golfers, in contrast, allocated the same mean durations to each gaze (about 1 s), independent of type of control (fixation, saccade, or tracking) or location (ball, club, target, or surface). In comparing hits to misses, there was an increased probability of hits if the golfers used express saccades to the club during preparation, and a steady fixation on the ball during the backswing/foreswing of the club, as well as a steady fixation on the surface during contact. These results suggest that with the acquisition of the putting skill, there are changes in gaze control, characterized by economy in the number of gaze shifts, the development of priority to specific gaze locations, and economy in the allocation of time between preferred gaze locations. In the discussion two reasons are proposed that may partially explain the results found here, as well as help further our understanding of the role of gaze in targetting skills.

Adult↗