Head Scanning of Patients with Homonymous Hemianopia
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2024-04-22
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Head contribution to horizontal gaze during outdoor mobility
in pedestrians with homonymous hemianopia
S Pundlik, P Shivshanker, A Kumar, M Tomasi, KE Houston, AR Bowers, E Peli, G Luo
What? – Measuring relative contribution of head movement to overall gaze shift by pedestrians with homonymous hemianopia (HH) in naturalistic walking
Why ? – Compensatory gaze scanning is key for safe mobility in HH; head turns presumably constitute a large part of gaze shifts, but real-world data is lacking
How? – Pedestrians with HH walked along a busy street wearing a gaze tracking system that measured gaze position with respect to the heading direction
Findings – Proportional head contribution increased with gaze for magnitudes < 65°, plateauing thereafter; larger head contribution to gaze at street crossings
Implications – First large scale analysis of relative composition of outdoor mobile gaze in HH; gaze scanning behavior could inform rehabilitation practices
Contact: shrinivas_pundlik@meei.harvard.edu
Head movements are major contributors of gaze shift in
HH pedestrians, especially at street crossings
Increasingly larger head turns employed to achieve gaze
shifts, up to a limit of around 65°
The limit of head contribution to gaze possibly related to
comfortable head turning limit
For largest gaze shifts, eye movements account for about
1/3
rd
of overall gaze magnitude
Supported in part by NIH grant EY031444 & DoD grant DM090420.
No relevant disclosures.
Large Gaze Shifts Key For Safe Mobility
Mobile Gaze Tracking System
Eye tracking: eye-in-head position
Differential signal from 2 inertial sensors, on hip and head
(hat), provides head movement with respect to the body
position (heading direction)
SLAM on eye-tracker scene camera frames for head pose
Fusion of head orientation estimates from SLAM and sensors
Gaze w.r.t heading direction = head + eye-in-head position
Gaze shift w.r.t. the heading direction related to safe
mobility in HH
Head movement presumably is a large contributor to the
overall horizontal gaze in outdoor walking scenarios
Real-world data about the relative contribution of head and
eye movements to outdoor mobile gaze is lacking
Frames from head-mounted camera from a Left HH subject
Captured scene Scene with Left side shaded
Looking
straight
ahead
Looking
Left into
the blind
field
Blindside
Gaze points
Scene to the Left
of the gaze point
is not visible
Large gaze scan
is needed to see
the approaching
car
Horizontal Gaze Signal During Outdoor Walking
Hprop: Proportion of Head Contribution to Gaze
Corresponding head and gaze positions obtained w.r.t. the body
midline (heading dir.) on the blind side and seeing side
Hprop computed from mean head position binned for each 10° gaze
increments on either side (excluding ±5° gaze bin around midline)
Results
Overall
Left HH
(LHH)
Left Hemi
-
Spatial
Neglect (LHSN)
Right HH
(RHH)
Num. of participants
19 6 6 7
Median age in years;
[25
th
– 75
th
percentiles]
53
[46
–
73]
50
[46
–
59]
50
[39 – 66]
63
[53 – 73]
% gaze
samples towards
the
Blind Side (>5
° magnitude)
50.4 % 51.6% 47.8% 52.2%
Hours of available
gaze data
- Crossings
- Sidewalk
6.9
2.5
4.4
1.6
0.6
1.0
2.6
0.9
1.7
2.6
1.0
1.6
Summary
Average Hprop
increased by 0.05
per 10° increment
in gaze until 60° bin
Hprop plateaued
thereafter
(slope < 0.01/10°
gaze increment)
Naturalistic walking on busy urban street during
daytime; included multiple pedestrian street crossings
Participants & Data Details
Average Hprop
significantly higher at
crossings (by 0.05),
compared to when
walking on the
sidewalk
Greatest difference
seen in RHH
Average Hprop
significantly higher
towards the
BlindSide in LHSN
(by 0.05), contrary to
the change in LHH
(diff. = -0.07) and
RHH (diff. = -0.04)
Factors involved in the analysis of Hprop:
Side w.r.t heading direction: Blind side vs. Seeing side
Walking location: crossings vs. sidewalk
Subject groups (LHH, LHSN, and RHH)
Head and gaze movements relative to the
mean heading direction (vertical dash &
dot black line at 0°) for a HH subject.
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