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[email protected]
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* University of Padova, Department of General Psychology, Via Venezia 8, 35131, Padova, Italy §Universität Regensburg, Institut für Psychologie, Universitätsstr. 31, 93053 Regensburg, Germany
Introduction
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Rebecca Camilleri*, Marcello Maniglia*, Andrea Pavan§, Gianluca Campana*
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The motion after-effect (MAE) has been shown to depend upon the functional integrity of visual area V5/MT, whereas earlier visual areas do not seem to be involved in this effect (Theoret et al., 2002). However, such results were obtained adapting to complex moving stimuli (e.g., spiral motion) and testing with stationary patterns.
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Investigating the neural regions involved in the storage of dynamic and static motion after effect using TMS
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Indeed, there are different types of MAE, for example it can be produced with simple translational or complex motion, and with static (sMAE) or dynamic (i.e., flickering, with no net motion direction) (dMAE) test stimuli. sMAE and dMAE show different spatio-temporal selectivity (Mather et al., 2008; Verstraten et al., 1998, 1999), suggesting the involvement of different neural substrates: an early locus of processing for sMAE, and a higher locus for dMAE.
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TMS was delivered via a Magstim Super-Rapid stimulator and a 70 mm figure-ofeight coil at 65% of intensity out of maximum intensity of 2 Tesla. A total of five pulses were delivered over a period of 500 ms (10 Hz). TMS was delivered over V2/V3, V5/MT and Cz during the ISI. Site localization was carried out on the basis of craniometric measures and phosphenes perception.
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With dMAE we found a significant difference between TMS over Cz and V5/MT (t15=5.39, p < .001), but no significant differences between TMS over Cz and V2/V3 (t15=2.07, p=.11), and no significant differences between TMS over V2/V3 and V5/MT (t15=1.23, p=.24).
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With sMAE we found a significant difference both between TMS over Cz and V2/V3 (t15=2.89, p=.022), and between TMS over Cz and V5/MT (t15=4.9, p=.0006), but no significant differences between TMS over V2/V3 and TMS over V5/MT (t15=0.41, p=.68).
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Task: Subjects were asked to judge the perceived duration of the MAE on the test stimulus by pressing the spacebar on a computer keyboard when the effect subjectively elapsed.
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In order to further investigate possible differences between the relevance of the tested neural substrates in sMAE vs. dMAE, we also ran Holm-Bonferroni corrected ttests separately for each Test Type.
Test Until response
Discussion and Conclusions
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Stimuli: Vertical gratings with 0.5 of Michelson contrast. For the sMAE the adapting stimulus had a spatial frequency of 2 cpd and a temporal frequency of 4.28Hz (velocity: 2.15 deg/s); the test stimulus was a static version of the adaptig stimulus. For the dMAE the adapting stimulus had a spatial frequency of 1 c/deg and a temporal frequency of 6Hz (velocity: 6 deg/s); the test stimulus consisted of a counterphase flickering grating with the spatial frequency of 1c/deg and a temporal frequency 3Hz.
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References
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Overall these data can be interpreted in terms of an involvement of both V2/V3 and V5/MT in the two types of MAE. Although there may be a tendency to have stronger involvement of V5/MT in dMAE, neurons involved in the generation of the two types of MAE do not seem to be strongly segregated in different neural structures, rather they are likely to rely on the same low- and intermediate-levels of motion processing. Indeed, the main locus of adaptation producing the MAE seems to depend more on other attributes of the motion stimulus: for example, sMAE produced by complex motion is caused by adaptation mainly at intermediate and high-levels of processing, where complex motion is normally processed (Théoret et al., 2002), whereas dMAE produced by rapid adaptation solidly rely on lower-level visual areas (Campana et al., 2011).
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Campana, Pavan, Maniglia, Casco (2011) The fastest (and simplest), the earliest: the locus of processing of rapid forms of motion aftereffect. Neuropsychologia, 49:2929-2934. Mather, Pavan, Campana, Casco (2008) The motion aftereffect reloaded. Trends in Cognitive Science, 12:481-487. Théoret, Kobayashi, Ganis, Di Capua, Pascual-Leone (2002) Repetitive transcranial magnetic stimulation of human area MT/V5 disrupts perception and storage of the motion aftereffect. Neuropsychologia, 40:2280-2287. Verstraten, van der Smagt, Fredericksen, van de Grind (1999) Integration after adaptation to transparent motion: static and dynamic test patterns result in different aftereffect directions. Vision Research, 39(4):803–810. Verstraten, van der Smagt, van de Grind (1998) Aftereffect of high-speed motion. Perception, 27(9):1055–1066.
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Subjects: 32 naïve subjects (16 subjects per MAE type) with normal or corrected-tonormal visual acuity participated in the experiment.
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A mixed-model ANOVA pointed out a significant effect of TMS (F1.5,45.6=16.96, p=.0001, ηp2=.36), but no significant effect of Test Type (static vs. dynamic; F1,30=0.58, p=.45, ηp2=.02) nor a significant interaction between TMS and Test Type (F1.5,45.6=0.97, p=.37, ηp2=.03).
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In this study, by using rTMS over V2/V3, V5/MT or Cz (control site), we investigated the locus of processing of sMAE and dMAE with simple translational motion.
