Differences in Early Stages of Tactile ERP Temporal Sequence (P100) in Cortical Organization during Passive Tactile Stimulation in Children with Blindness and Controls

Abstract

Compared to their seeing counterparts, people with blindness have a greater tactile capacity. Differences in the physiology of object recognition between people with blindness and seeing people have been well documented, but not when tactile stimuli require semantic processing. We used a passive vibrotactile device to focus on the differences in spatial brain processing evaluated with event related potentials (ERP) in children with blindness (n = 12) vs. normally seeing children (n = 12), when learning a simple spatial task (lines with different orientations) or a task involving recognition of letters, to describe the early stages of its temporal sequence (from 80 to 220 msec) and to search for evidence of multi-modal cortical organization. We analysed the P100 of the ERP. Children with blindness showed earlier latencies for cognitive (perceptual) event related potentials, shorter reaction times, and (paradoxically) worse ability to identify the spatial direction of the stimulus. On the other hand, they are equally proficient in recognizing stimuli with semantic content (letters). The last observation is consistent with the role of P100 on somatosensory-based recognition of complex forms. The cortical differences between seeing control and blind groups, during spatial tactile discrimination, are associated with activation in visual pathway (occipital) and task-related association (temporal and frontal) areas. The present results show that early processing of tactile stimulation conveying cross modal information differs in children with blindness or with normal vision.

Fig 1. Schematic representation of the stimulus presentation set up.

Stimuli are flashed in the LCD screen, read out by a camera mounted on the dark glasses, transformed into digital input and fed as tactile stimulation to the hand of the subject.

Fig 2. Event Related Potentials Following presentation of tactile presentation of spatial information.

Time frame to analyze the P100 component was 80–220 ms and it was determined by searching for the maximal amplitude in the respective time window at the Pz electrode. The BMA analysis was made opening a time window of -20 to +20 ms starting from the high amplitude pick measured in Pz electrode. The bottom of the figure displays the time blocks of the experimental design.

Fig 3. Grand average of Event Related Potentials in children with blindness (thick line) and their seeing counterparts (thin lines) following presentation of non-target stimuli on the line orientation (panel a) and letter recognition (panel b) tasks.

The time frames for analysis of the P100 component were determined by searching for the maximal amplitude in the respective time window at the Pz electrode between 80–220 ms.

Fig 4. Cortical intensity projection (BMA) mean maps obtained at the P100 windows following non-target stimuli presentation in the line orientation and letter recognition tasks.

Maximal intensity projection areas are displayed in red. Panel a: letter recognition in seeing children. Panel b: letter recognition in blind children. Panel c: line orientation in seeing children. Panel d: line orientation in blind children. Maximal intensity projection areas are displayed in red and yelow.

Fig 5. Statistical Mapping (SM) independent Hotelling T2 significant differences in P100 peak intensity between children with blindness and their seeing controls following presentation of non-target stimuli in the letter recognition (panel a) and line orientation (panel b) tasks.

Red color represents p < .05. For description of individual anatomical areas see Table 4.