Non-hexagonal neural dynamics in vowel space

Are the grid cells discovered in rodents relevant to human cognition? Following up on two seminal studies by others, we aimed to check whether an approximate 6-fold, grid-like symmetry shows up in the cortical activity of humans who "navigate" between vowels, given that vowel space can be approximated with a continuous trapezoidal 2D manifold, spanned by the first and second formant frequencies. We created 30 vowel trajectories in the assumedly flat central portion of the trapezoid. Each of these trajectories had a duration of 240 milliseconds, with a steady start and end point on the perimeter of a "wheel". We hypothesized that if the neural representation of this "box" is similar to that of rodent grid units, there should be an at least partial hexagonal (6-fold) symmetry in the EEG response of participants who navigate it. We have not found any dominant n-fold symmetry, however, but instead, using PCAs, we find indications that the vowel representation may reflect phonetic features, as positioned on the vowel manifold. The suggestion, therefore, is that vowels are encoded in relation to their salient sensory-perceptual variables, and are not assigned to arbitrary gridlike abstract maps. Finally, we explored the relationship between the first PCA eigenvector and putative vowel attractors for native Italian speakers, who served as the subjects in our study

Aging and Sensory Substitution in a Virtual Navigation Task

International audienceVirtual environments are becoming ubiquitous, and used in a variety of contexts–from entertainment to training and rehabilitation. Recently, technology for making them more accessible to blind or visually impaired users has been developed, by using sound to represent visual information. The ability of older individuals to interpret these cues has not yet been studied. In this experiment, we studied the effects of age and sensory modality (visual or auditory) on navigation through a virtual maze. We added a layer of complexity by conducting the experiment in a rotating room, in order to test the effect of the spatial bias induced by the rotation on performance. Results from 29 participants showed that with the auditory cues, it took participants a longer time to complete the mazes, they took a longer path length through the maze, they paused more, and had more collisions with the walls, compared to navigation with the visual cues. The older group took a longer time to complete the mazes, they paused more, and had more collisions with the walls, compared to the younger group. There was no effect of room rotation on the performance, nor were there any significant interactions among age, feedback modality and room rotation. We conclude that there is a decline in performance with age, and that while navigation with auditory cues is possible even at an old age, it presents more challenges than visual navigation

Path length.

<p>Top row: main effects; bottom row: interaction effects (ns). Significant effects marked with an asterisk.</p

The protocol.

<p>A schematic representation of the experimental protocol. Participants started with either a “stationary room” or “rotating room” block of trials, within which they performed the first half of the trials. The block was further divided into auditory and visual blocks, within each one, the participants performed five consecutive repetitions of each of two mazes.</p

Sample drawings.

<p>Sample drawings from a senior participant, who completed maze B in the auditory, stationary condition. Showing trials 1–5 for this maze, from left to right. A circle denotes the starting point, and a square denotes the end point. Inset: a sketch of the actual maze. This example demonstrates rotation (in all 5 trials) and mirroring (in the first 3 trials, on the left) of the drawings with respect to the actual maze.</p

Number of collisions.

<p>Top row: main effects; bottom row: interaction effects (ns). Significant effects marked with an asterisk.</p

Experimental setup.

<p>The participant is seated in the periphery of the Rotating Room, with comfortable head support. She is controlling the movement of the avatar through a virtual maze using the arrow keys of a laptop placed on a flat support located on her lap.</p

Average values (mean±SD) per performance metric.

<p>Average values (mean±SD) per performance metric.</p

Analysis of maze drawings.

<p>Values reported are means ± SD.</p

Number of pauses.

<p>Top row: main effects; bottom row: interaction effects (ns). Significant effects marked with an asterisk.</p