Reduced fields of view are neither necessary nor sufficient for distance underestimation but reduce precision and may cause calibration problems.
Watt et al. (Exp Brain Res, 2000, 135:411-416) suggested that a reduced field of view causes objects to appear closer than their physical distance. This suggestion is based on the observation that individuals terminated open-loop prehension prematurely when pretending to grasp a paper rectangle initially viewed through a reduced field of view. We tested Watt et al.'s suggestion in an open-loop pointing task. In experiment 1, 21 participants pointed at targets in three locations (20, 30 and 40 cm relative to the starting position) in three viewing conditions (full, 16 degrees and 4 degrees field of view). No difference in accuracy was found between conditions but the reduced field of view led to an increase in end-point variability across trials. We interpret these results as indicating that a reduced field of view decreases precision but does not necessarily affect object localisation. In experiment 2, we asked participants to reach-and-grasp a real object under the same three open-loop viewing conditions but without vision following movement onset. The experimental design ensured that haptic feedback was available, which could be used to calibrate reaching movements. We found that the reduced field of view caused no changes in grasp but we observed changes in the transport kinematics consistent with increased variability in the perceptual estimate of target location. Notably there were no changes in the spatial path (expected from movements to a closer location). In experiment 3, we repeated the Watt et al. design but removed vision and forced participants to rely on memory. In this condition we found the same undershoots as described by Watt et al. We conclude that a reduced field of view is neither necessary nor sufficient for underestimation and suggest that a reduced field of view decreases precision. This can cause participants to undershoot and/or alter the movement kinematics but we argue that such findings cannot be ascribed unambiguously to perceptual underestimation as they may reflect strategic alterations in behaviour.
Loftus
Andrea
A
School of Psychology, William Guild Building, University of Aberdeen, Aberdeen, AB24 2UB, UK.
Murphy
Susannah
S
McKenna
Isla
I
Mon-Williams
Mark
M
D001132:Arm / Q000294:innervation / Q000502:physiology; D001696:Biomechanical Phenomena; D003463:Cues; D003867:Depth Perception / Q000502:physiology; D005246:Feedback / Q000502:physiology; D006801:Humans; D009483:Neuropsychological Tests; D015588:Observer Variation; D009949:Orientation / Q000502:physiology*; D010775:Photic Stimulation; D011597:Psychomotor Performance / Q000502:physiology*; D012683:Sensory Deprivation / Q000502:physiology*; D013028:Space Perception / Q000502:physiology*; D014794:Visual Fields / Q000502:physiology*