The effects of arm and eye position on the perceived location of touches on the arm.
Vanessa Harrar, Laurence R Harris
Talk
Time: 2009-06-30 04:30 PM – 04:50 PM
Last modified: 2009-06-04
Abstract
Introduction:
The perceived position of auditory and visual stimuli shifts with head and eye position. Recently it has been shown that touches on the body also appear shifted when the head and eyes are not aligned indicating a coding system for touches that depend on the position of the eyes in the head. However, previous experiments that found eye position effects on localizing tactile and auditory stimuli required subjects to report the location of the stimuli in visual coordinates (relative to some visual scale). The transforms required by this method may have contributed to the effect of eye position reported. Therefore, we determined the effect of independently varying visual, arm, and body reference frames on the perceived location of touches using a novel technique that requires subjects to locate the position of touches relative to the arm.
Methods:
Eye position was controlled by having subjects fixate one of four lights separated by 10° arranged from left to right. Subjects’ left arms were placed over four tactors which were separated by 5 cm. The subject’s arm was positioned in one of three different orientations relative to their body: across the body, straight out (away from the body), or stretched out to the side. We drew lines on each subject’s forearm, dividing it into four equal segments, and asked subjects to report the segment (1-4) in which they were touched. This task did not require subjects to transform the touch into visual space.
Results:
As the eyes moved from left to right, the segment of arm in which a given touch was reported, shifted towards the wrist (for the left arm). The magnitude of the shift was smaller when measured in body coordinates than previously reported using a visual measure. The orientation of the arm relative to the body did not have a significant effect on the amplitude or direction of the eye-position-related shift. The perceived locations of the touches also varied with arm position. For both arm- and eye-related shifts, not all the areas of the arm were affected equally.
Conclusions:
Shifts of the perceived locations of touches related to eye position indicate that touches might be coded in a visual reference frame. The lack of systematic errors associated with arm position suggests that there are no additional localization errors associated with updating the position of the arm in space for judgments made in body coordinates. A comparison of tactile localization judgments made in visual versus body coordinates will be discussed and a model for tactile spatial perception will be presented.
The perceived position of auditory and visual stimuli shifts with head and eye position. Recently it has been shown that touches on the body also appear shifted when the head and eyes are not aligned indicating a coding system for touches that depend on the position of the eyes in the head. However, previous experiments that found eye position effects on localizing tactile and auditory stimuli required subjects to report the location of the stimuli in visual coordinates (relative to some visual scale). The transforms required by this method may have contributed to the effect of eye position reported. Therefore, we determined the effect of independently varying visual, arm, and body reference frames on the perceived location of touches using a novel technique that requires subjects to locate the position of touches relative to the arm.
Methods:
Eye position was controlled by having subjects fixate one of four lights separated by 10° arranged from left to right. Subjects’ left arms were placed over four tactors which were separated by 5 cm. The subject’s arm was positioned in one of three different orientations relative to their body: across the body, straight out (away from the body), or stretched out to the side. We drew lines on each subject’s forearm, dividing it into four equal segments, and asked subjects to report the segment (1-4) in which they were touched. This task did not require subjects to transform the touch into visual space.
Results:
As the eyes moved from left to right, the segment of arm in which a given touch was reported, shifted towards the wrist (for the left arm). The magnitude of the shift was smaller when measured in body coordinates than previously reported using a visual measure. The orientation of the arm relative to the body did not have a significant effect on the amplitude or direction of the eye-position-related shift. The perceived locations of the touches also varied with arm position. For both arm- and eye-related shifts, not all the areas of the arm were affected equally.
Conclusions:
Shifts of the perceived locations of touches related to eye position indicate that touches might be coded in a visual reference frame. The lack of systematic errors associated with arm position suggests that there are no additional localization errors associated with updating the position of the arm in space for judgments made in body coordinates. A comparison of tactile localization judgments made in visual versus body coordinates will be discussed and a model for tactile spatial perception will be presented.