soga2009: Predictive and postdictive mechanisms jointly contribute to visual awareness

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tags
Predictive Processing, Brain
source
paper
authors
Soga, R., Akaishi, R., & Sakai, K.
year
2009

This paper looks at the postdictive and predictive theories of perception, and provides experiments which suggest both these mechanisms could be present within visual processing.

  • FLC: Flash-lag condition, visual stimulus with a continuously changing feature (position/color) is presented, when another visual stimulus flashes briefly during the period of the features change. The trajectory of the feature before the flash is the same as the trajectory after. -> Additive contribution of the predictive and postdictive mechanisms to visual perception.
  • FTC: Flash-terminate condition, in which a flash stimulus is presented at the end of the continuously changing feature of another visual stimulus. -> Due to the feature change only existing before the flase, a perception in the flash-terminate condition reflects the predictive mechanism in visual awareness.
  • FRC: Flash-reverse condtion, a trajectory of continuously changing feature of a visual stimulus is suddenly reversed at the time of a flash stimulus. -> Interference between the predictive and postdictive mechanisms.
  • FIC: Flash-initiate condition, a flash stimulus is presented at the beginning of the continuously changing feature of another visual stimulus. -> reflects the postdictive mechanism in visual awareness.

Experiments

Experiment 1: Motion Flash-terminate Condition

Examined the effect of stimulus saliency on the flash-lag illusion in the motion flash-terminate condition by comparing a blurred wedge and salient white line conditions.

  • Results

    The blurred wedge showed a flash-lag effect of 1.8\degrees, suggesting that the predictive mechanism plays a role in perception of the position of moving stimulus in the FTC. On the other hand, the motion flash-lag effect was 0.09\degrees (not significant from 0\degrees ) for the salient line (consistent w/ previous findings). This result suggests stimulus saliency as a factor for predictive visual perception.

Experiment 2: Color flash-terminate condition

Examined the effect of stimulus saliency on the flash-lag illusion in the color FTC by comparing relatively ambiguous colors and relatively salient colors.

  • Results

    Predictive perception occurs in the FTC in the color domain. The changing color disk was perceived to be farther along the trajectory as compared to the flash disk (even though they were the same color).

Experiment 3: Effects of categorical perception on color FTC

Investigated the role of categorical perception of colors in the flash-lag illusion in the FTC. Thye manipulated the hue of the stimulus at the end of the continuously changing sequences.

  • Results

    Suggests that physical ambiguity and perceptual ambiguity of a stimulus enhances the predictive mechanism of visual perception.

Experiment 4: Mothion flash-lage effect in FLC, FTC, FRC, and FIC

Compared the magnitudes of the motion flash-lage effect in the FLC, FTC, FRC, and FIC using the the same blurred wedge as in Experiment 1.

  • Results

    The results support that joint contribution of prediction and postdiction to the perception of the position of a moving stimulus.

Experiment 5: Color flash-lag effect in FLC, FTC, FRC, and FIC

Compared the magnitudes of the color flash-lage effect in FLC, FTC, FRC, and FIC.

Experiment 6: Comparison of FTC and FIC in color domain

Teseted the possibility that the amount of the color flash-lag effect changes differently between the FTC and FIC depending on particular experimental varialbes. A positive result would account for the independent mechanisms for the flash-lag effect between FTC and FIC.

Discussion

Looking at the results, it seems that predictive and postdictive have an additive effect on visual perception with several factors weighting the effects.

Comments on significance

I’m concerned this paper does not provide compelling results (in terms of significance), w/ only 24 subjects with a subset used for each of eight studies. This does not feel like enough. While this is the case, I think they make a good case for their results in the end and looking at the other mentioned studies (Posner, Baldo, etc…). This seems to be a problem generally w/ neuroscience papers, and should be considered when thinking about these ideas.