Haptic discrimination in blind and low-vision children
Monica Gori, Giulio Sandini, Cristina Martinoli, David Burr
Poster
Time: 2009-07-02 09:00 AM – 10:30 AM
Last modified: 2009-06-04
Abstract
Propose of the study
Our recent results suggest that the development of multimodal integration of spatial information occurs late in childhood, around 8-10 years of age. Before integration is observed, either the haptic or visual system dominates, depending on the task: haptic for size and vision for orientation. If our suggestion that dominance is a side effect of sensory calibration, it should have direct consequences on children born without the possibility to use one sense to calibrate the other. For example, children without hands may show reduced precision in visual size judgments, as vision has not been calibrated against the more robust haptic sense; and conversely, children born blind or severely visually impaired should show reduced acuity for haptic orientation judgments.
Methods
We measured haptic discrimination thresholds for size and orientation discrimination in young (5-12 year-old) low-vision and blind children (with vision below 1/10), using the technique of Gori et.al. (Curr. Biol., 2008). For the size task children were presented successively with two plastic blocks and asked to judge haptically in 2IFC which was the taller (guessing if unsure). One stimulus (randomly first or second) was 55 mm high, the other of variable height between 48 and 62 mm. The proportion of trials where the probe was judged taller than the standard was computed for each probe height to produce psychometric functions, well fit by cumulative Gaussian functions (yielding PSE and SD). For the orientation task the procedure was similar to the previous one with the subject reporting haptically in 2IFC in which presentation the slope of the bar was steeper.
Results
For size discriminations, all subjects were very similar to the average thresholds for normally-sighted age-matched children. But for the orientation discrimination, all were far worse than normally sighted children: with thresholds of over 45 degrees. They could barely discriminate vertical from horizontal, and were very reluctant to do the task.
Conclusion
While this does not prove our theory about calibration, it is certainly consistent: if the haptic sense of orientation has never been calibrated against the more robust visual sense it does not develop the precision that normally sighted children have.
Our recent results suggest that the development of multimodal integration of spatial information occurs late in childhood, around 8-10 years of age. Before integration is observed, either the haptic or visual system dominates, depending on the task: haptic for size and vision for orientation. If our suggestion that dominance is a side effect of sensory calibration, it should have direct consequences on children born without the possibility to use one sense to calibrate the other. For example, children without hands may show reduced precision in visual size judgments, as vision has not been calibrated against the more robust haptic sense; and conversely, children born blind or severely visually impaired should show reduced acuity for haptic orientation judgments.
Methods
We measured haptic discrimination thresholds for size and orientation discrimination in young (5-12 year-old) low-vision and blind children (with vision below 1/10), using the technique of Gori et.al. (Curr. Biol., 2008). For the size task children were presented successively with two plastic blocks and asked to judge haptically in 2IFC which was the taller (guessing if unsure). One stimulus (randomly first or second) was 55 mm high, the other of variable height between 48 and 62 mm. The proportion of trials where the probe was judged taller than the standard was computed for each probe height to produce psychometric functions, well fit by cumulative Gaussian functions (yielding PSE and SD). For the orientation task the procedure was similar to the previous one with the subject reporting haptically in 2IFC in which presentation the slope of the bar was steeper.
Results
For size discriminations, all subjects were very similar to the average thresholds for normally-sighted age-matched children. But for the orientation discrimination, all were far worse than normally sighted children: with thresholds of over 45 degrees. They could barely discriminate vertical from horizontal, and were very reluctant to do the task.
Conclusion
While this does not prove our theory about calibration, it is certainly consistent: if the haptic sense of orientation has never been calibrated against the more robust visual sense it does not develop the precision that normally sighted children have.