Purpose: Perception of the external environment is dependent on input to multiple sensory modalities. Inputs from these modalities combine and interact to yield a final percept; each given a different weight under differing circumstances (Ernst & Banks, 2002). Inconsistencies in visuohaptic integration literature exist with regards to which sensory modality is given the greater weight (Ernst & Banks, 2002). The purpose of the present study was 1) to determine whether visual input influences haptic perception of line length and whether haptic input influences visual perception of line length. 2) To determine whether a produced estimate of perceived line length is more reliable with both visual and haptic exploration compared with either modality alone. 3) To determine whether produced estimates of line lengths yield greater integration of visual and haptic inputs when each emanates from a single source compared with two separate visual and haptic sources.
Methods: Two experiments were conducted. The first used two separate objects (one for visual input and one for haptic input). The second used a single object which the participant both visually and haptically explored. To test whether produced responses following bimodal exploration were more reliable than produced responses after unimodal exploration two methods were used. First, participants either simultaneously explored separate visual and haptic 3-dimensional lines of equal length or used either vision or touch alone to explore a 3-dimensional line. Second, participants simultaneously explored a single 3-dimensional line using vision and touch together or using either vision or touch alone. After exploration, participants reproduced a line that either matched what they saw or what they felt. All responses were made on a touch screen tablet notebook. To test whether visual input influenced haptic perception or whether haptic input influenced visual perception the same basic method was used but a discrepancy in length between the visual and haptic stimuli was added.
Results: Produced haptic responses were nearly double in length compared with produced visual responses. Inconsistent with previous studies, results for both experiments found that responses of bimodal exploration were not more reliable than responses of unimodal exploration. An influence of visual input on haptic perception of line length was found with separate visual and haptic objects only when participants made a visual response. An influence of visual input on haptic perception of line length and an influence of haptic input on visual perception of length was found for visual and haptic exploration of a single object regardless of the response modality.
Conclusions: 1) Produced haptic responses on a touch-screen notebook were double the length of comparable visual responses. 2) Visual input influences haptic perception of line length when visual and haptic sources are different. 3) Visual input influences haptic perception and haptic input influences visual perception when visual and haptic sources are the same. 4) Visuohaptic exploration with a common source promotes greater integration when compared with two sources, one for each modality. These findings can be applied to the development of visuohaptic technology. Realistic virtual environment and virtual training tool developers should be aware of the large discrepancy between participants’ visual and haptic responses when using a touch screen notebook.