Users with disability interact with augmentative and alternative communication devices, environmental control units, and computers via an access technology. While caregivers routinely exploit contextual information to interact meaningfully with individuals who are nonverbal and have severe motor impairments, access technologies to date have largely ignored context. Contextual factors include the environmental and personal factors in the model of functioning and disability introduced by The World Health Organization's International Classification of Functioning, Disability and Health in 2001.
We propose the use of mutual information as an objective means of measuring the impact of contextual factors on mechanical single switch usage. We show that common performance measures (e.g. sensitivity, specificity and response time) relating to switch use can be quantitatively unified within a mutual information measure. We exemplify the use of mutual information in the assessment of switch use in the presence of selected contextual factors. This information theoretic measure facilitates performance comparison amongst users and can potentially help in classification of contextual stimuli in terms of their impact (i.e. facilitating, barrier, neutral). Our examples with able-bodied participants and an individual with disability indicate that mutual information can be sensitive to changes in contextual factors. Mutual information may thus inform the design of individualized access technologies.