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Weber's law in tactile grasping and manual estimation: feedback-dependent evidence for functionally distinct
Shirin Davarpanah Jazi1, Matthew Heath2
1School of Kinesiology, The University of Western Ontario, Canada.
Brain and Cognition
|February 22, 2014
Summary
This study investigated how tactile actions and perceptions are processed using egocentric and allocentric frames of reference. Results partially support the somatosensory processing model, showing distinct reference frames for grasping versus manual estimation, influenced by tactile feedback.
Area of Science:
- Neuroscience
- Human Perception
- Somatosensory System
Background:
- The somatosensory processing model (SPM) proposes distinct reference frames for tactile actions and perceptions.
- Understanding these frames is crucial for explaining how we interact with objects through touch.
Purpose of the Study:
- To test the SPM's assertion that grasping relies on egocentric frames and manual estimation on allocentric frames.
- To investigate the influence of mechanoreceptor density and terminal tactile feedback on object size perception.
Main Methods:
- Experiment 1: Participants grasped and manually estimated objects on their forearm and palm, with post-estimation grasping to equalize tactile feedback.
- Experiment 2: Terminal tactile feedback was withdrawn during manual estimations on the forearm.
- Just-noticeable-difference (JND) scores and Weber's illusion were analyzed for both tasks and conditions.
Main Results:
- Grasping tasks showed no Weber's illusion, and JNDs violated Weber's law.
- Manual estimation tasks also showed no Weber's illusion, but JNDs adhered to Weber's law for the palm, not forearm.
- Removing tactile feedback during forearm manual estimations led to adherence to Weber's law.
Conclusions:
- Results partially support the SPM, indicating distinct egocentric and allocentric frames for grasping and manual estimation, respectively.
- The dissociation is not absolute and is modulated by terminal tactile feedback.
- Sensory consequences significantly influence the reference frames used in tactile perception and action.
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