Haptic Enumeration: Effects of Density and Distraction

Abstract

Currently, studies on haptic enumeration have predominantly utilized vibratory stimuli applied to the fingertips or stimuli of varying shapes and sizes, with relatively few studies utilizing braille as a stimulus. Due to braille's unique characteristics, multiple stimuli can be perceived simultaneously on a single fingerpad. Therefore, experimental results utilizing braille as a stimulus may provide valuable insight into the study of haptic enumeration. In our study, we employed braille as stimuli to investigate the haptic enumeration of visually normal adults. Participants actively touched the raised dots on the braille in a distal to proximal direction while wearing sound-attenuating headphones and a blindfold. We examined the effects of four variables on haptic enumeration: the number of perceived dots (1-12), density (compression and dispersion), distractor (minimum (0) and maximum (6) ), and hand and finger combination (homologous and non-homologous). Based on the experimental results, we drew the following conclusions and inferences: the perceived number showed a positive linear relationship with the actual number, and there was no evidence to support the bilinear fit model. However, based on the accuracy and confidence results, we speculated that haptic perception might have the subitizing ability for numbers one to three. Furthermore, based on this speculation, we deduced that participants used three enumeration modes during the enumeration process: groupitizing, counting, and estimation. Haptic enumeration appeared to be independent of non-numerical continuous magnitudes (density) in the current experimental paradigm. However, the interaction of density and the number of dots significantly affected the accuracy and confidence of haptic enumeration, probably due to the increased complexity of the stimuli in our experiment, which placed higher demands on cognitive abilities such as attention and working memory. Regarding the use of two fingers for number perception, it was found that homologous fingers were more beneficial for haptic enumeration than adjacent fingers. Additionally, we observed that directed attention played a significant role in haptic enumeration.