A Higher Order Motion Region in Human Inferior Parietal Lobule :Evidence from fMRI 뇌 과학 협동과정 이 성 하

introduction  How human perceive motion  Motion perception does not have a single underlying substrate, but result from the action of multiple, distinct mechanism. - Braddick(1974) Short- and long-range mechanism based on spatiotemporal factors - Chubb and Sperling(1988) Luminance based first-order motion processing Vs. non-Fourier second-order motion processing Difference in the computational mechanisms or neural substrates of human motion processing ?

introduction  Cavanagh(1992) & Sperling,Lu(1995)  Low-level, luminance based pre-attentive process vs. High-level salience based attentive process  Visual motion and attention  In most situation, things that move are brighter or darker than their surroundings (luminance difference strongly drive brain mechanisms for detecting motion)  higher order motion that can perform motion processing even when luminance cues are unavailable or misleading =>driven by salience of features (even when no luminance exists) or by willful attention to moving feature.

introduction  Motion processing area of previous study  Human middle temporal complex (hMT/V5+)  Human visual area (V3A)  Superior temporal sulcus (STS)  Several intraparietal sulcus (IPS) => Lower level motor system

introduction  The goal of the present study  To identify the neural substrates of the higher-level motor system  To contrast it to the traditional motion areas => fMRI responses to four kinds of stimuli designed to preferentially engaged higher- or lower- motor system

Main experiment 1 and Control 1  Hypothesis brain regions that reflect motion processing based on saliency will show greater activation in low- and high-green saturation conditions than in the medium-green saturation condition low-green (A), medium-green (B), high-green (C) saturation iso-luminant conditions

The higher-level feature tracking motor system: Main experiment 1 A) Right IPL ipsilaterally & hMT/V5+ bilaterally subtraction moving minus stationary in the different salience conditions B) Activity profile of R IPL (M: moving, S: stationary) =>active only for salience- defined motion C) R IPL, L hMT/V5+,R hMT/V5+ R IPL : salience based motion (higher motor system) hMT/V5+ : salience based motion + luminace based motion The higher-level motor system

 D) three group analysis  group 1 (highest attention sessions )  group3 (lowest attention sessions )  E) Functional profiles of right IPL  decreasing order of attention to the stimulus motion The higher-level feature tracking motor system: Main experiment 1 three separate group analyses (subject’s own estimated level of attention to the stimuli)

Right IPL Activation in Single Subject  A) subtraction moving minus stationary different salience conditions in the first main experiment  C) subtraction 7 Hz apparent motion minus 7 Hz control condition in the second main experiment =>The location of their right IPL activation in the two experiments matches very well

Bilateral Activation of IPL  A) right visual field  B) left visual field =>In both experiments, ipsilateral IPL is significantly (p < 0.05 corr.) activated

Comparison with the lower-level motion region : second control experiment  moving or stationary random texture pattern (The stimulus was located in the right visual field.)  motion regions (Sunaert et al., 1999) activation (A)  left-sided regions was larger for contralateral than ipsilateral visual field stimulation (B) First order motion: extract motion from moving luminance modulation.  activated by luminance based- motion (C)  STS,DIPSA :luminance defined motion 에 activation  DIPSM, PCI : isoluminant-isosalient condition 에 반응 안함

IPL region process other types of stimuli?  human lesion study (Battelli et al., 2001)  two dots apparent motion display (long range motion stimulus) might be processed by the IPL (R IPL lesion patients suffer from a bilateral deficit for long- range apparent motion, without deficit on lower order motion tests)  wondered whether the IPL region processes other types of stimuli for which a higher-level status had been proposed

Second main experiment-quartet display  The activation of the left IPL was weaker  The activity profiles of the two IPL regions are similar, with equally large activity for 7 Hz apparent motion in both visual hemifields C,D

Testing the conditions of main experiment 2 on the lower-level motion regions  Generally responsive to the 2Hz apparent motion & contralateral visual field stim.  hV3A, hMT/V5+ : responded to flicker  STS, PIC, DIPSM,DIPSA : Filcker response 가 거의 없음 cf) main exp. 1 에서 isosaliency- isoluminance condition 에 거의 반응 안한 영역과 일치 =>motion perception 에만 activation 영역

Second control experiment  the traditional motion regions : clear bias in favor of the contralateral visual field higher magnification in the center of the visual field  IPL random texture motion (M-S/S, full lines) apparent motion (AM-FL/ FL, dashed lines)

Response of IPL to another type of nonluminance- based motion, second- order motion  Second order motion Extract motion from moving stimuli ( luminance, feature, contrast, orientation…)  contrast-modulated checkerboard stimuli dissociation between first and second- order motion processing in patients experiment 5 revealed that in most lower-level motion regions, MR activity increased with motion coherence (hV3A exception)

 the higher-level motion IPL region responded little to these second-order motion stimuli, as was the case for first-order stimuli  significant IPL activation in the right but not the left hemisphere. This second- order motion site was located more ventrally than the higher-level motion region. Response of IPL to another type of nonluminance- based motion, second- order motion

Discussion  neural correlate of a higher-level salient feature-tracking motion system in the inferior parietal lobule  a slightly stronger sensitivity in the ipsilateral than central or contralateral field  selectively activated by another higher order, apparent motion stimulus (but not by second-order motion stimuli )  activation of the IPL region depended on the level of attention to the stimuli in general  traditional motion sensitive regions--hV3A, hMT/V5, STS, PIC, POIPS, DIPSM, and DIPSA  lower-level luminance-based system  processes both first-order and second-order motion stimuli  represents motion predominantly in the contralateral visual field, and magnifies the central part of the visual field

Discussion  lower- and higher order motion regions differ not in the stimuli processed (first or second order) but in the motion processing itself (Cavanagh, 1991)  the latter process being feature based, the former energy based  Although these are different processes, they might both compute a change of position over a change in time  the lower-level process over small ranges and the higher- level one over long ranges

Discussion  saliency & attention  although salience of a feature can be modulated by attention, the tracking of these features is not dependent on attention (Lu et al. (1999))  IPL region is clearly distinct from the human brain regions involved in directing exogenous and endogenous attention (Corbetta and Shulman, 2002).

Discussion  evidence of involvement of parietal cortex in motion processing  luminance-based stimuli : all activation sites were located in or near the intraparietal sulcus (IPS)  IPS located 17­19 mm medial, dorsal, and anterior to the higher- level IPL region  Both motion in the auditory and tactile modality activates a number of parietal regions (Griffiths et al., 1998; Lewis et al., 2000; Hagen et al., 2002)  Some of these motion regions overlap with lower-level visual motion regions (such as DIPSA)  auditory motion region and a tactile one, both in the IPL, are close to the higher-level visual motion region.