Cross-Sensory Facilitation Reveals Neural Interactions between Visual and Tactile Motion in Humans

Abstract

Many recent studies show that the human brain integrates information across the different senses and that stimuli of one sensory modality can enhance the perception of other modalities. Here we study the processes that mediate cross-modal facilitation and summation between visual and tactile motion. We find that while summation produced a generic, non-specific improvement of thresholds, probably reflecting higher-order interaction of decision signals, facilitation reveals a strong, direction-specific interaction, which we believe reflects sensory interactions. We measured visual and tactile velocity discrimination thresholds over a wide range of base velocities and conditions. Thresholds for both visual and tactile stimuli showed the characteristic “dipper function,” with the minimum thresholds occurring at a given “pedestal speed.” When visual and tactile coherent stimuli were combined (summation condition) the thresholds for these multisensory stimuli also showed a “dipper function” with the minimum thresholds occurring in a similar range to that for unisensory signals. However, the improvement of multisensory thresholds was weak and not directionally specific, well predicted by the maximum-likelihood estimation model (agreeing with previous research). A different technique (facilitation) did, however, reveal direction-specific enhancement. Adding a non-informative “pedestal” motion stimulus in one sensory modality (vision or touch) selectively lowered thresholds in the other, by the same amount as pedestals in the same modality. Facilitation did not occur for neutral stimuli like sounds (that would also have reduced temporal uncertainty), nor for motion in opposite direction, even in blocked trials where the subjects knew that the motion was in the opposite direction showing that the facilitation was not under subject control. Cross-sensory facilitation is strong evidence for functionally relevant cross-sensory integration at early levels of sensory processing.

Touch Interacts with Vision during Binocular Rivalry with a Tight Orientation Tuning

“…Arabzadeh et al [49] demonstrated that a visual flash presented near the fingers during a simple haptic discrimination task was able to reproduce the classical ‘dipper effect’ and improve near-threshold stimulus discriminability, as if the haptic signal had a direct input into the visual mechanism and provided the equivalent of a contrast pedestal. Similarly, in a speed discrimination task, Gori et al [50] showed cross-sensory facilitation between vision and touch that resulted in a two-fold improvement of discrimination thresholds that was specific for matched visuo-haptic motion direction. Together, these two findings suggest that the haptic signal in our experiment, which is likely to be broadly tuned after being remapped into visual coordinates and fed back to early visual cortex, effectively provided a contrast pedestal for vision, thereby improving visual orientation discrimination and producing a very sharp tuning.…”

Path integration in tactile perception of shapes

“…Humans are sensitive to tactile motion cues, which do not require temporal integration, such as the orientation, the direction, and the speed of motion [1][2][3]. To form a global motion percept, the tactile system spatially integrates the local motion signals provided by primary afferents across the skin [4].…”

Sensorimotor Modulation of Mood and Depression: In Search of an Optimal Mode of Stimulation

“…There is growing evidence for cross-modal synergism when stimulation from one modality is combined with that from another. After the seminal work by McGurk and MacDonald, 1976) that showed a cross-modal interaction between auditory and visual processing, cross-modal modulation and synergism have been reported across a number of sensory combinations such as between vision and audition (McDonald and Ward, 2000; Watanabe and Shimojo, 2001; Kayser et al, 2009), vision and olfaction (Zellner and Kautz, 1990; Zellner and Whitten, 1999; Koza et al, 2005; Dematte et al, 2009), vision and touch (Kennett et al, 2001; Ro et al, 2004; Gori et al, 2011), olfaction and audition (La Buisonniere-Ariza et al, 2012), somatosensation and audition, as well as audition and gustation (North, 2012). …”