Dissociation of Egocentric and Object-Centric Processing in Mental Rotation

1

Dissociation of Egocentric and Object-Centric
Processing in Mental Rotation
Tao, W.D.1, Yan, J.J.1, Wang, P.1, Zhou, L.1, and
Sun, H-J.2 1Southwest University, ChongQing,
China2McMaster University, Hamilton, Ontario,
Canada, sunhong_at_mcmaster.ca
Introduction
Experiment 1 Result and Discussion
Experiment 2 Result and Discussion

• Mental rotation can take either egocentric or
  object-centric forms.
• We explored a possible dissociation of these two
  processing mechanisms by
• using a special stimulus (hand), which may invoke
  a mental transformation of either the viewers
  own body (hand) or the visual display.

Back View
Palm View
Back View
Reaction time (ms)
Error rate ()
Reaction time (ms)
Reaction time (ms)
Error rate ()
Error rate ()
Rotate medially
laterally
laterally

• Material A was used in Exp1 while both A and B
  were used in Exp2.
• Respond through keyboard in Exp1.
• Respond by microphone in Exp2.

LR Task
A
B
SD Task
Experiment 1 Method
Degree of Rotation
Stimulus Back view of human hands which were
created by a 3D graphics software, was presented
at 45, 90, 135in medial (In-Rotation) or
lateral (Out-Rotation) direction from the upright
orientation in the picture plane. LR Task A
left or right hand was presented on the screen,
participant were asked to indicated the presented
hand was left or right one by pressing keyboard.
Design 2 (Hand left or right) 2 (Directions
of rotation medial or lateral ) 3 (Degree of
rotation 45, 90, 135) SD Task Pictures of
two hands were presented simultaneously on
screen, the left side of screen was always in an
upright hand and the right side was in several
different orientations of hand. Participants were
asked to indicate whether the presented pictures
were the same or different by pressing keyboard.
Design 2 (Match State match or no-match)2
(Hand left or right) 2 (Directions of rotation
medial or lateral ) (Degree of rotation 45,
90, 135) Participants N23 (11 male, 12
female).
Degree of Rotation
Degree of Rotation
Comparison between LR SD
Task
Task
Task
General Conclusion
Back vs Palm

• Effect of Direction of Orientation (we termed
  it our-rotation effect)
• LR task,
• In-Rotation (rotated medially) gt Out-rotation
• SD task, no difference
• Explanation
• LR task limited by the biomechanical
  constraints of the corresponding physical
  rotation especially in Out-Rotation
• SD task no such constrains
• Conclusion
• LR task egocentric frame of reference
• SD task object-centric frame of reference.

• The results of Exp1 and Exp2 suggest Ss use
  different spatial transformation mechanisms in LR
  (egocentric) and SD (object-centric) task.
• It appears that both the material of the body
  parts and paradigms of mental rotation determine
  the reference frame participants adopted and the
  Out-Rotation effect might serve as indicator for
  the dissociation of egocentric and object-centric
  mental rotation.

Experiment 2 Method
View
Stimulus the same to Exp 1 except that both the
back and palm picture of the hand were presented
at 25, 55, 85, 115, 145 LR task and SD
task the same to Exp1 except both back and palm
views were presented while the back of
participants hand facing up. Participants
responded by microphone Participants N16 (7
male, 9 female).

• The same patterns of result were observed as
  in Exp 1, for both back and palm views.
• LR task the back view gt palm view
• SD task no difference

Supported by research grants to HJS from the
Natural Sciences and Engineering Research Council
of Canada (NSERC), the Canadian Foundation for
Innovation (CFI) and the National Key Subject
Projects of Ministry of Education of China
Basic Psychology in Southwest University (Grant
Number XGZ413062).