Hemispheric specialization for spatial frequency ... - carole peyrin
[6] Ivry, R. B., & Robertson, L. C. (1998). The two sides of ... Moreover, preliminary results of the event-related functional Magnetic Resonance. Imaging (fMRI) ...
Hemispheric specialization for spatial frequency processing in natural scene perception and Hemianopia (a case study) Carole Peyrin , Sylvie Chokron , Olivier Gout and Christian Marendaz 1
1 Laboratory
1,2
2
1
of Psychology & NeuroCognition (CNRS - UMR 5105), Grenoble, France 2 Rothschild Ophtalmological Fondation, Paris, France
The hemispheric asymmetry hypothesis Experimental data suggest that visual analysis begins with a parallel extraction of several visual attributes at different scales/frequencies [1-4]. Neuropsychological studies have revealed that each hemisphere (at the level of temporo-parietal junctions-TPJ) could play a key role in spatial frequency processing: The right TPJ would be predominantly involved in low spatial frequency (LFs) analysis whereas the left TPJ would be involved in high spatial frequency (HFs) analysis [5]. Functional imagery data have, however, suggested that the cortical asymmetry in spatial frequency processing could appear earlier (at the occipital level) [6].
Research aims
HFs
This functional hemispheric asymmetry hypothesis of spatial frequency processing had been inferred from data obtained with the hierarchical form paradigm, without any explicit spatial frequency manipulation per se. The aims of the present research were to investigate, both in healthy subjects and neurological patients, the hemispheric specialization for spatial frequency processing in natural scene perception, by altering the picture frequency spectrum.
LFs
Neurospychological study
Cognitive Psychology study
Recently, Pambakian et al. [8] studied the natural scene processing of homonymous hemianopic patients and showed that only low filtered natural scenes recognition was more impaired in patients than healthy control subjects. Therefore, these results suggested that the primary visual cortex should be at least involved in low spatial frequencies processing.
Experiment Subjects 10 right-handed male students (5 per target scene).
Moreover, preliminary results of the event-related functional Magnetic Resonance Imaging (fMRI) study we are currently conducting suggest that the primary visual cortex would be asymetrically involved in spatial frequency processing: LFs processing shows a larger activation in the right primary visual cortex whereas HFs processing shows a larger activation in th left primary visual cortex.
Stimuli 2 natural scenes, each of them belongs to a different perceptual/semantic category (city and highway).
Procedure Categorization task; Go / NoGo response: Subjects had to press a button only if the target scene is present. The stimulus was displayed for 100 ms.
In this way, study of patients suffering from left or right homonymous hemianopia should allow us to specify the part played by the primary visual cortex in spatial frequency processing.
Spatial frequency components of scenes non-filtered scene (N) LFs scene (cut-off frequency: 4 cycles per degree) HFs scene (cut-off frequency: 6 cycles per degree)
Visual field of presentation / Hemisphere
A case study
Central visual field (CVF) Left visual field (LVF) / Right hemisphere (RH) Right visual field (RVF) / Left hemisphere (LH)
Experiment Stimuli and Procedure
Patient
The cognitive psychology study paradigm was presented to JM. The experimental paradigm was presented to JM on week before the intervention (pre-operative session) and six months after (postoperative session). The scenes were always presented in the healthy right visual field.
Patient JM who underwent an embolization of the right primary visual cortex. As a consequence, she suffered from a left homonymous hemianopia.
Results
Results 470
RH advantage
40
LFs
30
HFs
20 10
Categorization of LFs target scenes significantly faster in LVF/RH than in RVF/LH.
0
LH advantage
As expected, there was a significant interaction between the lateralized presentation (LVF and RVF) and the spatial frequency components of target scenes (LFs and HFs) [F(1;8)=10.57, p
1): The right TPJ would predominantly be involved in LFs analysis ... for spatial frequency processing when altering the picture frequency spectrum of natural.
the HFs contrast was increased (Fig. 1). A mask was used in order to prevent retinal persistence of the scene. The mask was built by the random sum of several ...
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[1] Frith, C. (1997) Brain, mind and behaviour in dyslexia. In: C. Hulme and M. Snowling, Editors, Dyslexia: Biology, cognition and intervention, Whurr Publishers, ...
superiority for spatial organisation. -50. -40. -30. -20. -10. 0. 10. 20. 30. 40. 50 exposure time of the priming scene. LH ad va nta ge in m s. R. H ad va nta ge in m.
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