Study shows blind people depend on timing cues for spatial estimations

The popular belief is that blindness enhances other senses such as hearing. Several studies show that while blind people’s other senses are not more acute, they do use auditory modality as a substitute to interpret some spatial representations. However, auditory precision might be impaired in congenitally blind individuals performing an audio-space bisection task.

A new study supported by the EU-funded weDRAW project has shown that the deficit disappears if congenitally blind individuals are presented with coherent temporal and spatial cues. The findings were recently published in the journal ‘iScience’. “Our results suggest that in some cases the brain may use temporal cues to infer spatial coordinates of the environment. A possible speculation is that it assumes the constant velocity of the stimuli and consequently uses temporal maps to solve spatial metric analysis.”

Quoted in a press release, lead author Monica Gori from the Istituto Italiano di Tecnologia explains: “This work teaches us that our audio-space representation is mediated by our visual experience. … In absence of vision, auditory spatial skills are not always enhanced – and in some cases, such as in the space bisection task studied here, these can be impaired.”

Time-space perception

Gori and her colleagues recruited 17 blind participants and 17 age-matched sighted people for their research. All participants were seated blindfolded in front of an array of 23 speakers. They were placed at a distance of 180 cm, spanning a visual angle of ±25 ° (0 ° represented the central speaker, with negative values on the left and positive values on the right). From left to right, three of the speakers played a beep and participants were asked to judge whether the second beep originated from a speaker closer to the first beep or the third one.

As summarised in the same press release, in the first round of the experiment, a uniform time delay of 750 ms followed each beep before another beep was played. In the next two rounds, delays between the beeps were timed to be either directly proportional to the distance between the speakers playing the beeps or indirectly proportional. Despite being blindfolded, sighted participants could generally judge the relative position of the sounds no matter how they were timed. However, timing had a significant impact on the judgement of the visually impaired participants. According to the press release, the researchers have preliminary data showing that young children use timing cues to judge spatial distance between sounds. “This may mean that the brain uses cross-sensory interactions during development to build spatial representations.”

The ongoing weDRAW (Exploiting the best sensory modality for learning arithmetic and geometrical concepts based on multisensory interactive Information and Communication Technologies and serious games) aims to investigate and design different types of digital learning environments using a range of senses like sight, sound, touch and movement to teach mathematical concepts to primary school children (aged 6-10 years). The project website notes that one of the scientific objectives is to “gain a deeper understanding of the rhythmic and motoric capabilities of typically developing, visual impaired, and dyslexic children at different stages of their development (6-7 yo and 8-10 yo) through carrying out psychophysical experiments.”