Obstacle detection display for visually impaired:Coding of direction, distance, and height on a vibrotactile waist band

Electronic travel aids (ETAs) can potentially increase the safety and comfort of blind users by detecting and displaying obstacles outside the range of the white cane. In a series of experiments, we aim to balance the amount of information displayed and the comprehensibility of the information taking into account the risk of information overload. In Experiment 1, we investigate perception of compound signals displayed on a tactile vest while walking. The results confirm that the threat of information overload is clear and present. Tactile coding parameters that are sufficiently discriminable in isolation may not be so in compound signals and while walking and using the white cane. Horizontal tactor location is a strong coding parameter, and temporal pattern is the preferred secondary coding parameter. Vertical location is also possible as coding parameter but it requires additional tactors and makes the display hardware more complex and expensive and less user friendly. In Experiment 2, we investigate how we can off-load the tactile modality by mitigating part of the information to an auditory display. Off-loading the tactile modality through auditory presentation is possible, but this off-loading is limited and may result in a new threat of auditory overload. In addition, taxing the auditory channel may in turn interfere with other auditory cues from the environment. In Experiment 3, we off-load the tactile sense by reducing the amount of displayed information using several filter rules. The resulting design was evaluated in Experiment 4 with visually impaired users. Although they acknowledge the potential of the display, the added of the ETA as a whole also depends on its sensor and object recognition capabilities. We recommend to use not more than two coding parameters in a tactile compound message and apply filter rules to reduce the amount of obstacles to be displayed in an obstacle avoidance ETA.</p

Vibrotactile perception of musical pitch

Previous vibrotactile research has provided little or no definitive results on the discrimination and identification of important pitch aspects for musical performance such as relative and absolute pitch. In this thesis, psychophysical experiments using participants with and without hearing impairments have been carried out to determine vibrotactile detection thresholds on the fingertip and foot, as well as assess the perception of relative and absolute vibrotactile musical pitch. These experiments have investigated the possibilities and limitations of the vibrotactile mode for musical performance. Over the range of notes between C1 (32.7Hz) and C6 (1046.5Hz), no significant difference was found between the mean vibrotactile detection thresholds in terms of displacement for the fingertip of participants with normal hearing and with severe/profound hearing impairments. These thresholds have been used to identify an optimum dynamic range in terms of frequency-weighted acceleration to safely present vibrotactile music. Assuming a practical level of stimulation ≈10dB above the mean threshold, the dynamic range was found to vary between 12 and 27dB over the three-octave range from C2 to C5. Results on the fingertip indicated that temporal cues such as the transient and continuous parts of notes are important when considering the perception of vibrotactile pitch at suprathreshold levels. No significant difference was found between participants with normal hearing and with severe/profound hearing impairments in the discrimination of vibrotactile relative pitch from C3 to C5 using the fingertip without training. For participants with normal hearing, the mean percentage of correct responses in the post-training test was greater than 70% for intervals between four and twelve semitones using the fingertip and three to twelve semitones using the forefoot. Training improved the correct responses for larger intervals on fingertips and smaller intervals on forefeet. However, relative pitch discrimination for a single semitone was difficult, particularly with the fingertip. After training, participants with normal hearing significantly improved in the discrimination of relative pitch with the fingertip and forefoot. However, identifying relative and absolute pitch was considerably more demanding and the training sessions that were used had no significant effect