JOBB FÉLTEKE DOMINANCIA A VIZUÁLIS

STATISZTIKUS TANULÁS KEZDŐFÁZISÁBAN

József Fiser, Matthew E. Roser*, Richard N. Aslin# & Michael S.

Gazzaniga*

Brandeis University, University of Rochester# and

Dartmouth College*

Great diversity of proposed hemispheric

specializations

Hemispheric differences in object perception

•For highly familiar objects:

RH metric and positional information LH abstract categorical information •RH visual form information LH conceptual associations

•RH early information (low SF) LH late information (high SF)

Object perception requires visual feature learning

•First, visual scenes are interpreted via already learned object features

•Next, search for new specific spatial co-occurrences and new arrangements among elements (emergence of new feature combinations) occurs•Finally, explicit access to a new feature by developing associations and categorical and semantic meaning

Right hemisphere

Left hemisphere

Question:

Can the process of learning new

visual features be linked to

differential involvement of the

two brain hemispheres?

Six base-pairs

Fit three base-pairs into 3 X 3 grid

The basic paradigm

Visual feature = spatio-temporal conjunction of separate shapes

Testing phase

• 2AFC task• Base-pair vs. Non-base pair

A

B

E

F

I J

A

B

Base-pair Non-base pairs

IF

Split the base-pairs

Modifying the paradigm

GHC

D

K L

A

B

F

E

I J

2 deg

Modified test phase

Ipsilateral:

• Practice: RH Test: RH• Practice: LH Test: LH

Contralateral:

• Practice: RH Test: LH• Practice: LH Test: RH

Four lateralized test types

Subjects

• Normal subjects: Sixteen college students

• Callosotomy patient: V. P.

(Corballis et al. Neurology 2001)

SpleniumRostrum

Experimental procedure for normal subjects

Practice:

•144 scenes alternating randomly between the right and left visual fields

•Eye-movements monitored by iView to verify fixation (and hemifield stimulation)Test:

•Six test trials in each of the four test types (Ipsi, Contra) x (RH, LH)

Results with normal subjects

Equal learning in all conditions interhemispheric transfer

40

50

60

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80

90

100

40

50

60

70

80

90

100

Practice: RH LH LH RH

Test: RH LH RH LH

Normal

Ipsilateral Contralateral

Chance

V.P.'s testing schedule

1st day: practice

2nd day: practice, ipsilateral tests, practice,

ipsilateral tests

3rd day: practice, ipsilateral tests, practice,

ipsilateral tests

4th day: practice, contralateral tests

5th day: practice, contralateral tests

Data collection in five days

40

50

60

70

80

90

100

40

50

60

70

80

90

100

Practice: RH LH LH RH

Test: RH LH RH LH

Normal

Split brain

Ipsilateral Contralateral

•Contralateral: No interhemispheric

information transfer•Ipsilateral: Strong right hemisphere advantage

*

Chance

Results with the split brain patient

Conclusions

•The initial phase of extracting spatial statistical regularities from the visual input is dominated by right hemisphere processes

•These results predict a shift of relative brain activity from the right to the left hemisphere as visual perception shifts from naïve observation to a knowledge-based interpretation of the scene

•Visual statistical learning does not transfer across split hemispheres even when some limited transfer of higher-level word-related information is possible