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Magnetoencephalogram (MEG) correlated with perceptual binding of color and motion

Magnetoencephalogram (MEG) correlated with perceptual binding of color and motion. Kaoru Amano 1 , Shin’ya Nishida 2 , and Tsunehiro Takeda 1. 1. University of Tokyo 2. NTT Communication Science Laboratories. motion. color. motion. color. Color motion asynchrony. Perception. Stimulus.

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Magnetoencephalogram (MEG) correlated with perceptual binding of color and motion

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  1. Magnetoencephalogram (MEG) correlated with perceptual binding of color and motion Kaoru Amano1, Shin’ya Nishida2, and Tsunehiro Takeda1 1. University of Tokyo 2. NTT Communication Science Laboratories

  2. motion color motion color Color motion asynchrony Perception Stimulus Stimulus synchrony (SOA = 0 ms) Perceptual asynchrony (When color reversals and motion direction reversals are physically in phase, they are not perceived to be in synchrony.) 250 ms Stimulus asynchrony (SOA = 100 ms) Perceptual synchrony (When motion directions reversal precedes color reversals by about 100 ms,they are perceived to be in synchrony) 250 ms SOA Moutoussis & Zeki (1997)

  3. Purpose • To find the neural activities correlated with perceptual synchrony and binding of color and motion • Comparison of MEGs between the condition of perceptual synchrony (SOA=100 ms) and that of perceptual asynchrony (SOA=0 ms) • Averaged waveforms • Wavelet analysis of time-frequency domain • Psychophysical experiments of the perceptual synchrony and binding of color and motion • To test psychophysically-proposed models, by seeing • The difference in latency of motion response and color response • The effect of alternation rate on MEG responses • The effect of temporal structure on MEG responses

  4. Visual stimulus • Color • Test (4 s): Color was reversed between red and green at 2Hz • Pretest (1 s): a green pattern • Always stationary • Motion • Test (4 s): Motion direction was reversed between expansion and contraction at 2Hz • Pretest (1 s): a stationary pattern • Always green • Color + Motion (SOA 0 ms) • Test (4 s): Color and motion direction were reversed at 2Hz with no physical delay (perceptual asynchrony) • Pretest (1 s): a stationary green pattern • Color + Motion (SOA 100 ms) • Test (4 s): Color and motion direction were reversed at 2Hz with a color delay of 100ms (perceptual synchrony) • Pretest (1 s): a stationary green pattern color + motion SOA ・・・ stationary Cont. ・・・ Exp. Exp. 1 s 0.5 s MEG measurement 5 s trigger • Concentric half rings • SF: 1.1 cycle/deg, contrast：50% • Red or Green • Stationary or Expantion/Contraction • velocity: 3 deg/s

  5. MEG recording and analysis • Ten male subjects were employed. • MEG recording • Whole head MEG system (Yokogawa, PQ244OR) with 230 axial-z sensors and 70 x 3 vector sensors • Sampling rate: 625 Hz, Filter: 0.3-200 Hz • The number of average: 100 times • Pre-trigger: 1000 ms, post-trigger: 4000 ms • Wavelet analysis • Sensor output in each trial was convolved with complex Morlet wavelets and was averaged across all trials (Tallon-Baudry, 1996). • The time varying energy for each frequency was corrected by the pre-trigger interval of 500 ms. • The results of right or left occipital channels were averaged (34 channels for each). • Dipole source localization • 230 axial-z sensors over the whole head were used for the estimation. • Analysis was conducted for averaged MEG filtered at gamma band (20-60 Hz). • Goodness of Fit (GOF) should be larger than 80 %.

  6. Psychophysical experiment Binding task Synchrony task Identify the color presented during expanding motion Tell whether color and motion were perceived to be in phase Color fast Motion fast Color fast Motion fast In-phase response (%) Red response (%) Averaged across all subjects (n=10) Color delay SOA (ms) Color delay SOA (ms) More successful binding of color and motion for SOA=100 ms than for SOA=0 ms. More synchronous perception of color and motion for SOA=100 ms than for SOA=0 ms.

  7. Interactions of averaged waveforms Waveform interaction, defined by [Color+Motion]-([Color]+[Motion]), averaged between 1000 and 3750 ms and across occipital 68 sensors and subjects (n=10) Color Motion MEG amplitude (fT) Color+Motion (SOA 0 ms) MEG amplitudes (fT) Color+Motion (SOA 100 ms) Latency (ms) • Peaked response to each stimulus change (every 250 ms) were found except for ‘motion’ condition. • There was no difference in the magnitude of waveform interaction between the condition of perceptual asynchrony (SOA=0ms) and the condition of perceptual synchrony (SOA=100 ms).

  8. Interactions in time-frequency domain • Interactions in 20-40Hz were larger under the condition of perceptual synchrony (SOA=100ms) than under the condition of perceptual asynchrony (SOA=0ms). • The effect was significant for 30-35 Hz in left hemisphere (p=0.034) Frequency domain interactions, defined by [color+motion]-([motion]+[color]), averaged between 1000 and 3750 ms and across occipital 34 left sensors and subjects (n=10) Color Motion Frequency (Hz) Color+Motion (SOA 0 ms) TF Energy Color+Motion (SOA 100 ms) 20-25 30-35 40-45 50-55 25-30 35-40 45-50 55-60 Latency (ms) Frequency band (Hz)

  9. Dipole source localization Color，Color + Motion (without filter) Color + Motion (20-60Hz) 168 ms 3120 ms • Dipoles were estimated in the similar visual area for “Color” and “Color+Motion” with both SOAs. • Dipole estimation for motion direction reversal was not successful because of the low S/N. • Magnetic field maps of 6/10 subjects indicated the activities in the occipital areas • Their dipoles were mainly estimated around calcarine sulcus. • The dipole amplitudes were generally larger under the condition of perceptual synchrony than under the condition of perceptual asynchrony.

  10. Dependency of temporal structure • Perceptual asynchrony depends on the temporal structure of the stimuli (first-order change versus second-order change) rather than the attribute type (color versus motion). • C1+P2: Motion delay (color motion asynchrony) • C1+P1 or C2+P2: No delay • C2+P1: Color delay Enhanced 20-40Hz responses might be correlated not with perceptual synchrony but with physical asynchrony Nishida and Johnston, 2002 Using C1P1 or C2P2 stimulus will make it clear whether enhanced gamma responses are correlated with perceptual synchrony or physical asynchrony

  11. First- and second-order change of color and position Nishida and Johnston, 2002 First-order change (transitions) C1P1 (no delay) color Defined by two points in time Position C1P2 (motion delay) C2P1 (color delay) Second-order change (turning point) color Defined by three points in time C2P2 (no delay) Position (Motion)

  12. Psychophysical experiment (C1P1) Synchrony task Binding task Identify the color when the rings were at the outward position Tell whether color change and position change were perceived to be in phase Color fast Motion fast Color fast Motion fast Red response (%) In-phase response (%) Color delay SOA (ms) Color delay SOA (ms) Averaged across all subjects (n=6) More synchronous perception of color and motion for SOA=0 ms than for SOA=100ms. More successful binding of color and motion for SOA=0ms than for SOA=100ms.

  13. Interactions in waveforms and time-frequency domain (C1P1) • Interactions of averaged waveforms were very similar between the two SOA conditions. • Interactions in 20-30Hz were larger under the condition of perceptual synchrony (SOA 0 ms). Frequency domain interactions, defined by [C1P1]-([C1]+[P1]), averaged between 1000 and 3750 ms and across occipital 68 sensors and subjects (n=6) Waveform interactions, defined by [C1P1]-([C1]+[P1]), averaged between 1000 and 3750 ms and across occipital 68 sensors and subjects (n=6) TF Energy MEG amplitudes (fT) 20-25 30-35 40-45 50-55 25-30 35-40 45-50 55-60 Frequency band (Hz)

  14. Psychophysical experiment (C2P2) Binding task Synchrony task Identify the color increasing during expanding motion Tell whether color change and motion were perceived to be in phase Color fast Motion fast Color fast Motion fast In-phase response (%) Green response (%) Averaged across all subjects (n=6) Color delay SOA (ms) Color delay SOA (ms) More successful binding of color and motion for SOA=0ms than for SOA=100ms. More synchronous perception of color and motion for SOA=0 ms than for SOA=100ms.

  15. Interactions in waveforms and time-frequency domain (C2P2) • Interactions of averaged waveforms were very similar between the two SOA conditions. • Interactions in 20-30Hz were larger under the condition of perceptual synchrony (SOA 0 ms). • The effect was significant for 20-25 Hz in right hemisphere and 20-25, 25-30 Hz in left hemisphere (p=0.049, p=0.032, p=0.0065 respectively). Frequency domain interactions, defined by [C2P2]-([C2]+[P2]), averaged between 1000 and 3750 ms and across occipital 68 sensors and subjects (n=6) Waveform interactions, defined by [C2P2]-([P2]+[C2]), averaged between 1000 and 3750 ms and across occipital 68 sensors and subjects (n=6) TF Energy MEG amplitudes (fT) 20-25 30-35 40-45 50-55 25-30 35-40 45-50 55-60 Frequency band (Hz)

  16. Discussions Previous studies on the binding of visual attributes • Electrophysiological studies on animals • When two superimposed gratings that differ in orientation and drift in different directions are perceived as a single pattern (pattern motion), synchronization between neurons sensitive to each motion direction was increased (Castelo-Branco et al., 2000) • Under the condition of binocular rivalry, cells driven by the winning eye show a significant correlation (Fries et al., 1997) • EEG or MEG studies on human • Gamma band responses were enhanced when subjects perceived illusory (Kaniza) triangle (Tallon-Baudry et al., 1996) • Gamma band responses were enhanced when subjects perceived Dalmatian dog hidden in black blobs (Tallon-Baudry et al., 1997) 20-40 Hz responses were enhanced when C1 and P2 were perceived to be in synchrony (SOA=100ms), while 20-30 Hz responses were enhanced when C1 and P1 or C2 and P2 were perceived to be in synchrony (SOA=0ms). 20-30Hz responses, slightly lower than the gamma band (>30Hz), might be correlated with perceptual binding of color and motion

  17. Models of color motion asynchrony Psychophysically-proposed models of color motion asynchrony • Latency difference model (Moutoussis & Zeki, 1997) • Color and motion are processed in different areas, and the processing time difference between color and motion leads to perceptual asynchrony • Time marker model (Nishida & Johnston, 2002) • Temporal localisation judgements are made by using temporal markers assigned to salient changes • Hybrid model (Clifford et al, 2003; Bedell et al., 2003) • Separate mechanisms for temporal synchrony and binding Give some suggestions on these models by analyzing MEG amplitudes and latencies

  18. Time marker model Nishida & Johnston, 2002 • Perceptual motion delay occurs only for rapid alternations • Reaction times are not different between color and motion Latency model can not account for color motion asynchrony Temporal localisation judgements are made by using temporal markers assigned to salient changes • Accurate temporal order judgement for slow alternations result from matching between first order changes (color change) and second order changes (motion direction reversal) • Color motion asynchrony at rapid alternations result from matching between first-order changes (color change and position change) • Color change, position change (motion) • First-order change • Time marker can be allocated even at rapid alternations • Motion direction reversal • Second-order change • Time marker is difficult to be allocated at rapid alternations

  19. Verification of the models • The effect of alternation frequency on the color change (C1) response and motion direction change (P2) response. • According to the time marker model, the response to motion reversal becomes less salient for higher frequencies while the saliency of color change does not change largely. • Comparison of MEG amplitudes and latencies between color change (C1), color direction change (C2), position change (P1), and motion direction change (P2) at 2 Hz • Are there any difference in latency between MEG to P2 and C1 • Does the temporal structure of stimuli affect MEG amplitudes and/or latency?

  20. color color motion motion Dependency on alternation rate • Increasing alternation rate did not decrease color response. • Motion response reduced at higher alternation rate (2Hz). NS 0.25 Hz * RMS (fT) Peak RMS (fT) 2 Hz 0.25Hz 2Hz 0.25Hz 2Hz RMS (fT) color motion Average of peak RMS values at 250-500, 500-750 ms. time (ms) Consistent with the time marker model

  21. Dependency on temporal structure: Latency • The latency difference between C1 and P2 is consistent with the latency model, and is also consistent with the time marker model given MEG primarily reflects the response to first-order temporal changes. • Similarity in latency found between C1 and P1, and between C2 and P2 is consistent with time marker model, but the latency model cannot predict these results. • MEG latency was apparently shorter (but in fact longer, considering the short stimulus cycles) for color change (C1) than for motion direction change (P2). • MEG latency was affected not by stimulus attribute but by temporal structure Alternation rate: 2Hz Latency (ms)

  22. Dependency on temporal structure: Amplitude • MEG amplitude was smaller for motion direction change (P2) than for position change (P1), and for color direction change (C2) than for color change (C1). Alternation rate: 2Hz Amplitudes (fT) Compatible with the hypothesis that MEG primarily reflects the response to the first-order temporal change and the first-order change in P2 and C2 were less salient than that in P1 and C1.

  23. Suggestions on models • P2 response reduced at higher alternation rate (2Hz), though increasing alternation rate did not decrease C1 response. • MEG latency was affected not by stimulus attribute (color vs. motion) but by temporal structure (first-order vs. second-order). The MEG responses support the time marker model (and hybrid models) more than the latency model.

  24. Summary • MEG responses for simultaneous alternations in color and motion direction were measured. • 20-40 Hz responses were enhanced when C1 and P2 were perceived to be in synchrony (SOA=100ms), while 20-30 Hz responses were enhanced when C1 and P1 or C2 and P2 were perceived to be in synchrony (SOA=0ms). • MEG responses were compatible with the time marker model of color-motion asynchrony (Nishida and Johnston, 2002) indicating matching of salient events.

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