Perceptual Bistability in Occluded Digital Numbers: a Behavioral Study

2536 

Abstract Submission 

Junxiang Luo¹, Isao Yokoi¹, Hiromasa Takemura^1,2,3

¹National Institute for Physiological Sciences, Okazaki, Japan, ²The Graduate Institute of Advanced Studies, SOKENDAI, Hayama, Japan, ³Center for Information and Neural Networks (CiNet), Advanced ICT Research Institute, NICT, Suita, Japan

Junxiang Luo  
National Institute for Physiological Sciences
Okazaki, Japan

Isao Yokoi  
National Institute for Physiological Sciences
Okazaki, Japan

Hiromasa Takemura  
National Institute for Physiological Sciences|The Graduate Institute of Advanced Studies, SOKENDAI|Center for Information and Neural Networks (CiNet), Advanced ICT Research Institute, NICT
Okazaki, Japan|Hayama, Japan|Suita, Japan

Number characters are essential visual stimuli widely used in modern society. Understanding the behavioral and neural mechanisms for processing number characters will improve the current understanding of how visual information can be hierarchically processed to establish semantic recognition of numbers. We found that the digital number, one of the popular number designs that frequently appear in our daily lives, can be a useful tool to study the recognition of number characters since a partial occlusion can cause perceptual ambiguities and induce bistable interpretations (Figure 1A). Here, we report a behavioral study investigating how the perceptual bistability of occluded digital numbers can be manipulated by adapting to certain types of visual stimuli.

Fifteen adult human participants (8 females and 7 males) with normal or corrected-to-normal vision participated in the experiment after a written informed consent. Participants were instructed to see the visual stimuli appearing in a display, while maintaining a viewing distance of 65cm. Visual stimuli were designed by MATLAB Psychtoolbox extensions (Brainard, 1997; Pelli, 1997; Kleiner, 2007). During the experiment, participants were asked to maintain fixation to the point appearing at the center of the screen. Figure 1B describes the timeseries of the experiment. Participants were firstly asked to look at adaptation stimuli (digital numbers, Arabic numbers, digital elements, kanji characters, and white noise) for a certain amount of time, and were then asked to report whether a test stimulus (occluded number) presented afterwards can be seen as 6 or 8, or other numbers. Participants repeated 20 trials for each stimulus condition. In the data analysis, we calculated the bias index (BI): BI=(CR₆ - CR₈)/(CR₆ + CR₈), where CR₆ and CR₈ indicate the choice ratio of perceiving "6" and "8", respectively. We performed the Krusukal-Wallis one-way analysis of variance for testing statistical significance by comparing the bias index in different adaptation conditions and calculated Cohen's d for evaluating the effect size.

The report from one participant clearly shows the perceptual biases caused by adaptation, after adapting to number 6 or the element corresponding to 6, the perceptual interpretation of occluded character tends to be 8; while adapting to number 8 tend to generate perception of number 6 from the occluded test stimuli (Figure 2A). Figure 2B depicts the population results of the BI from 15 participants. We found that adaptation to digital and Arabic numbers caused significant perceptual bias for test stimuli (occluded characters), in a consistent manner among participants. We also found statistically significant evidence of perceptual bias in the digital elements adaptation condition, although the effect size (d=1.96) was much smaller than those in digital and Arabic number conditions (d=8.22 and 4.11, respectively). We did not find a statistically significant perceptual bias in the condition of kanji characters adaptation.

Our results demonstrate that adaptation to number characters affects bistable perception of partially occluded digital number stimuli. We found that this effect can also be seen when adaptation stimuli were Arabic numbers and digital elements, suggesting that this perceptual bistability mainly originates in the middle level of visual processing, where shapes and number forms are encoded (Tanaka, 1996; Kravitz et al., 2013). A lack of evidence in kanji characters suggests that higher-order stage that represents numerosity or semantics did not take a significant role in generating this phenomenon (Nieder, 2016). The results of this behavioral study will provide an experimental design for future studies, testing how much activities in cortical regions processing shape and number forms (Shum et al., 2013; Cai et al., 2023) can be correlated with subjective experience in number perceptions.

Space, Time and Number Coding ²

Perception: Visual ¹

Cognition

Perception

Vision