Research on Self-Esteem

Research on Self-Esteem

Flexible Retinotopy: MotionDependent Position Coding in the Visual Cortex David Whitney, Herbert C. Goltz, Christopher G. Thomas, Joseph S. Gati, Ravi S. Menon, Melvyn A. Goodale Science, 2003, Vol 302, 878881. Say something first Background of Retinotopy A anti-tradition fMRI result How the authors exclude other possible explanations Seeking help from behavioral

designs A bit of my experiments (Possible Connection) Discussion Visual areas subdivision Visual maps in the macaque monkey brain derived from single neuron electrophysiology Visual maps in the human brain

derived from fMRI The occipital lobe contains many maps of the visual world fMRI for Dummies are Slides from Jody Culhams PPT file. fMRI for Dummies Macaque Retinotopy Source: Tootell et al., 1982 Retinotopy: Adjacent points of the visual world fall on adjacent

points on the retina and are represented in adjacent points in the visual cortex fMRI for Dummies Transforming the Map to Polar Coordinates N x direction Polar Angle fMRI for Dummies Taking Care of All the Flips in V1

Left Occipital Lobe N Right Occipital Lobe N One visual area has one complete map of visual space Here is the map in primary visual cortex, V1 fMRI for Dummies V2 is a mirror image of V1

Left Occipital Lobe Right Occipital Lobe fMRI for Dummies Retintopy: Flickering Checkerboard ROTATING WEDGES 8 Hz flicker (checks reverse contrast 8X/sec) good stimulus for driving visual areas subjects must maintain fixation (on red dot) fMRI for Dummies

Retinotopy Source: Sereno et al., 1995, Science fMRI for Dummies A anti-tradition fMRI result Fig 2 E Traditional Retinotopy works in Flickering Gabor stimulus with different physical position Flickering patterns used, its physical position is displaced by the amount of the visual illusion (from Fig. 1E).

A anti-tradition fMRI result Moving Gabor stimulus with same physical position Fig 1 E Vision Illusion (not a new finding) The perceived position of the patterns is shifted in the direction of the moving texture. (E) The psychophysically measured magnitude of the illusion. Will it create the same Retinotopy as flickering one? A anti-tradition fMRI result

Fig 2 A-D None-Traditional (flexible) Retinotopy Cortical surface, Right hemisphere, Occipital region. (Increasing eccentricity in the direction of the yellow arrow. (C) inward outward =orange (significantly activated). Lower panel, event related average for orange

voxels (D) (ourward inward =blue). Excluding other possible explanations A: Is this strange retinotopy caused by that Illusion Perception (a blurry edge is needed)? Fig 4-A Patterns containing motion with sharply

defined borders. Although no illusory position shift, the same pattern of activation was Excluding other possible explanations B: Is spatially localized attention responsible for the results? No, details please see Figure 7S.

Controlling spatially localized attention. Subjects need performed a difficult attentionally demanding task at the fixation point (Counting how many red and blue flashes were presented and whether there were more red or blue flashes). The pattern of activation was identical to that in the first experiment. This rules out the possibility that the results are attentionally modulated. Seeking help from behavioral designs Trailing edge mechanism as Whitneys explanation True reason underlying flexible Retinotopy: Peak activity always occurs at the trailing edges, which is the pro

duct of a mechanism that operates more strongly on the trailing edge. But what mechanism? It seems no Clear answer Provided . Three behavioral An imbalance in motion processing between the traili experiments: ng and leading edges. Behavioral designs did not directly explain fMRI result, it seems parallel but not explanatory. 1 Figure 4S. The position shift at the trailing edge is more larger than that of the leading edge.

2 Figure 5S. The luminance contrast of the trailing edge is not just reduced, but also appears distorted. (if contrast reduced, how it creates peak activation?) 3 Figure 8S. The illusion of induced motion was Seeking help from behavioral designs Figure 4S. Figure 5S. Figure 8S. Seeking help from behavioral

designs Trailing edge mechanism as Whitneys explanation Link between position shift and contrast decrease Partially Explain the illusion in Experiment 1: Because the contrast of the trailing edge is perceptually reduced, the midpoint of the pattern as a whole appears displaced toward the leading edge, causing Illusion. Links between Trailing effect and Flexible Retinotop The peak activation always occurs closer to the trailin g edge of moving patterns (or origin of the motion), r egardless of perceived position (Illusion independent) . This is verified by previous and following fMRI results

Excluding another possible explanation and further verification C: Is it possible that optic flow in previous stimuli responsible for the results? So, how about no exp/con optic flow, only trailing edge? Patterns did not contain exp/con optic flow. Motion originated from either the vertical or the horizontal meridian. Upper Stimulus:

Trailing Edge-Vertical Leading Edge-Horizontal Lower Stimulus: Trailing Edge-Horizontal Leading Edge-Vertical Excluding another possible explanation and further verification So, how about no optic flow, only trailing edge? Fig 4-B V1/V2 border represents the motion

along vertical angle, while motion along horizontal angle should appear within V1. Implication of this study: the results demonstrated a clear dis sociation: fMRI activation did not correlate wit h what subjects perceived, showing t hat the BOLD response is not a nece ssary correlate of perception. Did not provide the answer (?) why the trailing edge creates peak activation.

It seems correlative? but not causal? A bit of my experiments Possible Connection? What we are interested? 1 What will happen if we use moving dot pattern i nstead of Gabor or grating? 2 What will happen if we use two trailing edges or two leading edges together? Will the trailing effect be strengthened or neutra lized? 3 Any other possible explanations that could acco unt for fMRI results besides trailing effect? A bit of my experiments

Possible Connection? Three behavioral experiments: E1: o Vs o CP Vs CF E2: o -- Vs o -CP+S Vs CF+S E3: o Vs o EXP (CP-CF) V s CON (CF-CP) Task: discriminating the motion-defined border. The design is similar to Whitley et.

Figure 4S. A bit of my experiments Possible Connection? In order to match expansion /CP with contraction /CF, we created the contraction sequence first, then get the expansion simply by reversing the frame order of contraction. This guarantees that the two patterns are completely matched in properties,

such as dot density near the perceived border line. Unsignificant result of perceived border shift. E1: o Vs o CP Vs CF A bit of my experiments Possible Connection? E2: o -- Vs o -CP+S Vs CF+S

Significant result in the direction of forward movement. It seems adding stationery point facilitates the forward movement. A bit of my experiments Possible Connection? E3: o Vs o EXP (CP-CF) Vs CON(CF-CP) Significant result, bu t opposite to the dire

ction of forward mov ement. There must exist a v ery strong mechanis m who can reverse t he whole pattern, wh ich favor forward mo vement direciton. What is it ? A bit of my experiments Possible Connection? E3: o Vs o EXP Vs CON According to Whitneys finding, the trailing effect shoul

d be in the same direction with the forward movement . Unexpected Result: the trailing effect NOT been stre ngthened (increasing the Forward Movement Effect) or neutralized (only Forward Movement Effect). Section Width of left/right to border line: E3: > Vs > Left S > Right S in width (Forward Movement Eff ect) A bit of my experiments Other Possible Explanation? E3: o Vs o EXP Vs CON Noisiness hypothesis: the perceived border line

of CON seems more noisy than that of EXP. Maybe not, if so, E2 should has similar effect. Adding stationery points seems facilitate the forward movement instead of reducing it. Contrast reduction hypothesis: the contrast of CON border line is reduced compared with that of EXP. Maybe not, if so, the contrast reduction should facilitate the forward movement direction (according to Whitneys result) or make the threshold different between EXP/CON (but not). A bit of my experiments Other Possible Explanation? E3: o Vs o EXP Vs CON

Anisotropic sensitivity to motion direction: Vision sy stem is more sensitive to CentriPetal rather than CentriFu gal motion direction. CP > CF Experimental evidences: By measuring coherence thre shold using a signal-to-noise technique, Raymond, 1994 f ound that sensitivity to CP moving stimuli was significantl y better than to CF moving stimuli. Dyre & Andersen, 1997,found that perceived heading wou ld drift toward the relatively weaker hemi-field when ther e is an imbalance of image velocity between the two hem i-fields of an optic flow pattern. o (CP > CF, drift to Right) o (CF < CP, drift to Left)

Discussion Any other possible explanation to the fMRI result besides trailing effect ? Patterns did not contain exp/con optic flow, but it does contai n Centripetal Centrif ugal motion dimensio n. Trailing edge= CP Leading edge= CF Maybe CP>CF be poss ible candidate?

Discussion Sub regions preference to different motion type ? Fig 3 (D) Activation produced by the flickering patterns alone. The activity in (A) overlapped in the flickering condition. (E) Event-related average for the entire ROI. Although no difference in the event-related activity

for the three conditions (inward motion, outward motion, and flickering) for this ROI as a whole, but it did not ruin out the possibility that sub-regions in this area have preference to CP/CF

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