spatial perception and hemispheric lateralization – a...
TRANSCRIPT
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Spatial perception and hemispheric lateralization
– a factor analysis approach
Ineke J.M. van der Ham & Albert PostmaHelmholtz Institute, Utrecht University
Evanston, 15 June 2008
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Spatial relations Spatial relations within and between objects (Kosslyn, 1987)
Categorical vs. Coordinate
Hemispheric lateralization Categorical – left hemisphere (LH) Coordinate – right hemisphere (RH)
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Dot-bar task Visual half-field task
Categorical Coordinate
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Dot-bar results Findings
Coordinate RH advantage is often foundCategorical LH advantage is less often found Coordinate mostly more difficult than
categoricalResults depend on specific stimulus featuresPerceptual vs. working memory tasks
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Experiment 1 Interval length variation is suggested to be of
importance: Categorical bias – stronger over time
Postma et al. (2006) dot – circle task, 500 ms/2000 ms/5000 ms
Coordinate – immediate decay Huttenlocher et al. (1991), Werner & Diedrichsen, (2002)
Congruency with functional properties(Kosslyn, 1987)
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Stimuli 4 categories 4 coordinates
van der Ham et al., 2007
S1 S2
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Trialsequence
S1
S2
+
S1
750 ms
500 ms
150 ms, central
0/1500/4500 ms
+
S2
500 ms
150 ms, lateral
2000 ms
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Visual field * retention interval Instruction * visual field * retention interval
At 500 ms: instruction * visual field Within instruction: main effect retention interval
Cat. 500 ms/2000 ms < 5000 ms Coo. 500 ms < 2000 ms / 5000 ms
850
950
1050
1150
1250
cat coo cat coo cat coo
500 2000 5000
retention interval and visual field
RT (in ms)
LVFRVF
retention interval and instruction
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Discussion Visual field * instruction effect found in 500 ms
Main effect in categorical instruction
Decay over timeCoordinate: quick decayCategorical: decay later in time
How does this outcome relate to the dot-bar paradigm?
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Experiment 2:Task battery Hemispheric lateralization found in many tasks
in different domains spatial perception
Bringing such tasks together is of importance Speculation on (evolutionary) origin of the
hemispheric differences and (causal) relations between them
Interpretation of individual differences
For spatial tasks this has not been done thoroughly
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Three spatial perception tasks
Spatial frequency identificationHigh frequency → LH
low frequency → RH (e.g. Sergent, 1983)
Local – global processingLocal features → LHGlobal features → RH (e.g. Van Kleeck, 1989)
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Dot-bar taskCategorical → LHCoordinate → RH (Hellige & Michimata, 1989)
Additional task: a version of cross-dot design Interval of 500 ms Adapted stimuli Match-to-sample working memory Enables comparison between two cat – coo tasks
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Combining the tasks
Theory: Double filtering of frequency model (Ivry & Robertson, 1997)
Practice: Experiments based on combining features of two of these three paradigms Cat-coo blurred with different frequencies (Okubo &
Michimata, 2002, 2004)
Local – global with different frequencies (e.g. Badcock, 1990)
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Method
47 subjects (20 male) 4 tasks
3 perceptual (frequency, local-global, cat-coo)150 ms stimulus presentation (3° from centre)
1 match-to-sample working memory (cat-coo)150 ms stimulus 1 central, and 150 ms stimulus 2 lateral (3° from centre)
RT was used for analysis
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Lateralization index in performance (RVF-LVF)/(RVF+LVF)
Value between -1 (LVF-RH largest) and 1 (RVF-LH largest) RT:
-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
0.04
LSF HSF global local coo p cat p coo mts cat mtsLI
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Factor analysis 3 factors, 80.24% of the variance explained:
Factor Subtasks Factor loading
1 Categorical mts LVF +0.77 Categorical mts RVF +0.73 Coordinate mts LVF +0.84 Coordinate mts RVF +0.89 Local LVF +1.00 Local RVF +0.98 2 High spatial frequency LVF -0.98 High spatial frequency RVF -0.99 Low spatial frequency LVF -1.03 Low spatial frequency RVF -1.14 Global LVF -0.52 Global RVF -0.55 3 Categorical p LVF -0.81 Categorical p RVF -0.79 Coordinate p LVF -1.04 Coordinate p RVF -1.05
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Factor analysis 2
Only tasks showing hypothesized lateralization effect:
Factor Subtasks Factor loading
1 Categorical mts LVF +0.87 Categorical mts RVF +0.86 Coordinate mts LVF +0.82 Coordinate mts RVF +0.82 Local LVF +0.81 Local RVF +0.82 Global LVF +0.83 Global RVF +0.78
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Discussion
For all tasks 3 factors were found Related to task complexity or level of processing Categorical-coordinate perception is separate
Comparing the two cat – coo tasks the new cross-dot task reflects the hypothesized
lateralization effect, the dot-bar task clearly does not Careful consideration when using such cat-coo tasks
in further experiments, a working memory design appears to be more appropriate than a perceptual design
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Categorical-coordinate WM and local-global load on a single factorStronger relationship between the two than
with spatial frequency has been proposed before (Vauclair et al., 2006)
this suggests a link between the two, unaffected by frequency
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Discussion points
Current theoretical claims seem insufficient to explain these results
Other factors might underly these patternsSuggestions?
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Thank you for your attention.
Questions?