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SUMMARY:Sensorimotor and perceptual representations engaged when performin
 g and observing object manipulation tasks - Randy Flanagan\, Department of
  Psychology\, Queen's University\, Canada
DTSTART:20061201T130000Z
DTEND:20061201T140000Z
UID:TALK5849@talks.cam.ac.uk
CONTACT:Cordula Becker
DESCRIPTION:In this talk I will examine links between action and perceptio
 n in the context of object manipulation. I will first show that the sensor
 imotor system and the perception system maintain independent representatio
 ns of object weight used to guide manipulatory actions and judge weight re
 spectively. I will then provide evidence that\, when observing an actor pe
 rform manipulation tasks\, observers implement “motor plans” that clos
 ely match those of the actor.\n     We have examined sensorimotor and perc
 eptual representations of object weight in the context of the size-weight 
 illusion whereby the smaller of two equally weighted objects is judged to 
 be heavier when lifted. We have shown that when repeatedly lifting such ob
 jects\, people initially scale their fingertip forces to object size but q
 uickly adapt their force output to the true object weights and thus exhibi
 t accurate sensorimotor predictions. Nevertheless\, the size–weight illu
 sion persists. This indicates that the sensorimotor system can operate ind
 ependently of the perceptual system. We have also shown that the size-weig
 ht illusion can be inverted through extensive (multi-day) practice lifting
  inverted objects for which weight varies inversely with size. Thus\, perc
 eptual representations of object weight can be altered but at a far slower
  rate than sensorimotor representations. We conclude that both the normal 
 and inverted forms of the illusion arise from a mismatch between expected 
 and actual weight at the perceptual level.\n     According to the direct m
 atching hypothesis\, observers understand the actions of others by engagin
 g a mechanism that maps an observed action onto motor representations of t
 hat action. We have directly tested this notion by examining observers’ 
 eye movements when watching object manipulation tasks. We have shown that 
 the coordination between their gaze and the actor’s hand is strikingly s
 imilar to the gaze-hand coordination when they perform the task themselves
 . In both cases\, gaze is proactively directed to key landmarks important 
 for hand movement planning and control. These findings suggest that during
  action observation\, people implement task-specific eye movement programs
  that are directed by representations of the manual actions required in th
 e task. We have also examined observers’ gaze behaviour when watching un
 predictable actions. We show that observers still use\, or attempt to use\
 , proactive eye movements. Although the gaze behaviour of observers and ac
 tors differs in the kinematic details\, it is similar in terms of the goal
 s of the eye movement.
LOCATION:Seminar Room (ground floor)\, Craik-Marshall Building
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