Distinct Contributions of Genes and Environment to Visual Size Illusion and the Underlying Neural Mechanism

Neuroimaging evidence of visual-vestibular interaction accounting for perceptual mislocalization induced by head rotation

Significance

A fleeting flash aligned vertically with an object remaining stationary in the head-centered space would be perceived as lagging behind the object during the observer's horizontal head rotation. This perceptual mislocalization is an illusion named head-rotation-induced flash-lag effect (hFLE). While many studies have investigated the neural mechanism of the classical visual FLE, the hFLE has been hardly investigated.

Aim

We measured the cortical activity corresponding to the hFLE on participants experiencing passive head rotations using functional near-infrared spectroscopy.

Approach

Participants were asked to judge the relative position of a flash to a fixed reference while being horizontally rotated or staying static in a swivel chair. Meanwhile, functional near-infrared spectroscopy signals were recorded in temporal-parietal areas. The flash duration was manipulated to provide control conditions.

Results

Brain activity specific to the hFLE was found around the right middle/inferior temporal gyri, and bilateral supramarginal gyri and superior temporal gyri areas. The activation was positively correlated with the rotation velocity of the participant around the supramarginal gyrus and negatively related to the hFLE intensity around the middle temporal gyrus.

Conclusions

These results suggest that the mechanism underlying the hFLE involves multiple aspects of visual-vestibular interactions including the processing of multisensory conflicts mediated by the temporoparietal junction and the modulation of vestibular signals on object position perception in the human middle temporal complex.

Threat shapes visual context sensitivity selectively through low-spatial-frequency channels

Threat has long been supposed to affect human cognitive processing including visual size perception. Whether such threat-related modulation effect varies as a function of spatial frequency is largely unexplored. Here we used low- or high-pass filtered threatening animal and fearful face images as primes and measured their effects on the processing of the Ebbinghaus illusion. Results showed that threatening-animal primes relative to neutral ones significantly decreased the illusion magnitude in low-spatial-frequency rather than in high-spatial-frequency ranges. However, fearful- and neutral-face primes had a comparable effect on the illusion magnitude in both spatial frequency ranges. Notably, when inhibitory transcranial magnetic stimulation was applied to the left temporo-parietal junction (TPJ), fearful-face primes significantly decreased the illusion magnitude in low-spatial-frequency rather than in high-spatial-frequency ranges. However, the opposite pattern of results was observed with right TPJ stimulation. The findings suggest that threat shapes basic aspects of visual perception in a spatial frequency-specific manner, possibly via magnocellular projections from both subcortical and cortical fear-processing systems to early visual cortex.

Intrinsic excitability of human right parietal cortex shapes the experienced visual size illusions

Converging evidence has found that the perceived visual size illusions are heritable, raising the possibility that visual size illusions might be predicted by intrinsic brain activity without external stimuli. Here we measured resting-state brain activity and 2 classic visual size illusions (i.e. the Ebbinghaus and the Ponzo illusions) in succession, and conducted spectral dynamic causal modeling analysis among relevant cortical regions. Results revealed that forward connection from right V1 to superior parietal lobule (SPL) was predictive of the Ebbinghaus illusion, and self-connection in the right SPL predicted the Ponzo illusion. Moreover, disruption of intrinsic activity in the right SPL by repetitive transcranial magnetic stimulation (TMS) temporally increased the Ebbinghaus rather than the Ponzo illusion. These findings provide a better mechanistic understanding of visual size illusions by showing the causal and distinct contributions of right parietal cortex to them, and suggest that spontaneous fluctuations in intrinsic brain activity are relevant to individual difference in behavior.

Number comparison under the Ebbinghaus illusion

A series of studies show interest in how visual attributes affect the estimate of object numbers in a scene. In comparison tasks, it is suggested that larger patches are perceived as more numerous. However, the inequality of density, which changes inversely with the area when numerosity remains constant, may mediate the influence of area on numerosity perception. This study aims to explore the role of area and density in the judgment of numerosity. The Ebbinghaus illusion paradigm was adopted to induce differences in the perceived, rather than the physical, area of the two patches to be compared. Participants were asked to compare the area, density, and the number of the two patches in three tasks. To this end, no PSE (point of subjective equality) bias was found in number comparison with randomly distributed dots, although a significant difference was revealed in the perceived area of the two patches. No PSE bias was found in the density comparison, either. For a comparison, density and number tasks were also conducted with regularly distributed dots. No PSE bias was found in density comparison. By contrast, significant PSE bias showed up in number comparison, and larger patches appeared to be more numerous than smaller patches. The density mechanism was proposed as the basis for number comparison with regular patterns. The individual Weber fractions for regular patterns were not correlated with those for random patterns in the number task, but they were correlated with those for both patterns in the density task. To summarize, numerosity is directly sensed, and numerosity perception is not affected by area inequality induced by the Ebbinghaus illusion. In contrast, density and area are combined to infer numerosity when the approximate numerosity mechanism is disrupted by dot distribution.