  Buddhist authors, unlike their Brahmanical opponents, make a clear  distinction between the activity or faculty of sensing  (indriyagocara) and the medium which implements it, as for  instance in distinguishing between the faculty of vision  (cakṣurvijñānadhātu) and the visual  system (cakṣurdhātu). Moreover, the senses are  conceived as receptacles of experience  (indriyādhiṣṭhāna) rather than  physical organs interacting with empirical objects. Instead of  treating the senses as the faculties of an internal agent, the  Buddhists regard them as instruments or mediums joining together the  external spheres of sensory activity with the internal spheres of  perception (see Abhidharmasamuccayabhāṣya ad I, 4.). In the Treasury of Higher Knowledge  (AKBh ad I, 17), Vasubandhu provides the following list to  account for the causal relations that obtain between the sensory  systems and their bases or domains of activity  (āyatana): 