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Effects of luminance contrast, averaged luminance and spatial frequency on vection

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Abstract

Changing the speed, size and material properties of optic flow can significantly alter the experience of vection (i.e. visually induced illusions of self-motion). Until now, there has not been a systematic investigation of the effects of luminance contrast, averaged luminance and stimulus spatial frequency on vection. This study examined the vection induced by horizontally oriented gratings that continuously drifted downwards at either 20° or 60°/s. Each of the visual motion stimuli tested had one of: (a) six different levels of luminance contrast; (b) four different levels of averaged luminance; and (c) four different spatial frequencies. Our experiments showed that vection could be significantly altered by manipulating each of these visual properties. Vection strength increased with the grating’s luminance contrast (in Experiment 1), its averaged luminance (in Experiment 2), and its spatial frequency (in Experiment 3). Importantly, interactions between these three factors were also found for the vection induced in Experiment 4. While simulations showed that these vection results could have been caused by effects on stimulus motion energy, differences in perceived grating visibility, brightness or speed may have also contributed to our findings.

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Data availability statement

All data generated or analyzed during this study are included in this published article and its supplementary information files.

Notes

  1. As the visibility was mainly caused by the change of the luminance contrast of the motion stimulus. Experiments 2 and 3 had constant luminance contrast, so perceived visibility was not examined in those experiments.

  2. In Experiments 1 and 3, the averaged luminance of the motion stimulus was constant, so the subjective brightness was not examined in those two experiments.

  3. In Experiment 4, there was only one speed of motion stimulus, so we did not measure the perceived speed.

  4. At present, we cannot execute motion–energy simulation for different spatial frequency conditions because our simulation was based on the behaviour of a single optimal motion detector to a specific frequency, applied for a specific spot.

  5. When manipulating averaged luminance in this experiment, the following constraints needed to be satisfied: averaged luminance × (luminance contrast + 1) < maximum luminance and averaged luminance × (luminance contrast − 1) < minimum luminance. A mid-level of luminance contrast was therefore chosen, so we could examine the effects of a wider range of average luminance.

  6. We did not adjust the averaged luminance in this experiment, and set the contrast to 0.899 (as measured by the luminance meter). In pilot testing, we found that if we used to same contrast as Experiment 1 (i.e. 0.999), our participants were likely to experience motion sickness in the highest spatial frequency condition. Thus, we instead used a 0.899 contrast to examine the effects of a wide range of stimulus spatial frequencies on vection.

  7. In Experiment 4, we did not use the lowest and highest levels of averaged luminance from Experiment 2 for practical reasons. This was because: (1) participants were more likely to become motion sick in 17.035 cd/m2 conditions, and (2) little/no vection was experienced under 1.590 cd/m2 conditions.

  8. We selected low and middle levels of luminance contrast deemed to be the most appropriate for our Plasma TV display.

  9. These stimulus spatial frequencies were chosen based on empirical observations in Experiment 3 that higher spatial frequencies tended to decrease vection strength.

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Acknowledgements

This study was supported in part by the Japan Society for the Promotion of Science KAKENHI (21K03135, NS).

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Correspondence to Xuanru Guo or Takeharu Seno.

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Communicated by Melvyn A. Goodale.

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Appendix

Appendix

Simulating of the effects of luminance contrast and averaged luminance based on the motion energy model.

figure a

To estimate the effect of luminance contrast and averaged luminance, we ran simulations based on the motion energy model of Adelson and Bergen (1985) in a simple situation. These simulations were similar to those examining the effects of framerate on the motion energy in a recent paper by Fujii et al. (2017).

Consider horizontal grating (distance between wave nodes = w) moving downward at a constant velocity (= v) as in Fig. (a). The locus of the grating motion (= M) can be represented as an inclined sinusoidal grating in spatial–temporal space. Luminance contrast and averaged luminance are equal to those of the original grating (Fig. (c)).

According to the motion energy model, a motion detector in the spatial–temporal system can be represented as a quadrature pair of Gabor filters (D0 and Dp/2) in Fig. (b) (like those used by Fujii et al. 2017). The width of central positive field of D0 equals the width between nodes of the moving grating instead of the bar width. The mathematical details of these simulations are the same as those of the referenced method, except that we used sinusoidal grating motion (instead of bar motion) and controlled luminance (instead of the frame rate) (see details in the “Appendix 1” of Fujii et al. 2017).

The results of these simulations are shown in Fig. 11 in the main text. The horizontal axis indicates either the Michelson luminance contrast (Simulation 1) or the averaged luminance (Simulation 2), and the vertical axis shows the motion energy (relative to the maximum motion energy = 1). Averaged luminance was held constant in Simulation 1 and luminance contrast was held constant in Simulation 2. These results show that motion energy increases slowly as function of both luminance contrast and averaged luminance at the lower ranges and then gradually accelerates at the higher ranges.

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Guo, X., Nakamura, S., Fujii, Y. et al. Effects of luminance contrast, averaged luminance and spatial frequency on vection. Exp Brain Res 239, 3507–3525 (2021). https://doi.org/10.1007/s00221-021-06214-5

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