The hypothesis of labelled detectors (or ‘lines’) is the present-day version of the basic Müller - Helmholtz doctrine. Müller's dictum of specific energy of nerves stated: “the same internal cause excites (…) in each sense the sensation peculiar to it”. Helmholtz made ‘the cause’ external to the body and postulated that all knowledge about the world thus comes through the senses. The key word is specificity. The strong version of the hypothesis must treat detection - identification as a single task: a stimulus would be identified whenever it is detected. The weak version requires only that we identify a specific mechanism by which both detection and identification are achieved, even though the latter may require additional processing. In the general case, the strong version (with its ludicrous ‘grandmother cell’ as the neural substrate) finds little support. Detection and recognition of complex shapes (letters, faces, etc) aside, even discrimination between simple increments and decrements of luminance is difficult to attribute directly to a specific mechanism (in this case, the activity in either ON or OFF systems, respectively). This is demonstrated by experiment 1 reported here. However, perception of relative depth seems to conform to the strong version of the hypothesis, as experiment 2, also reported here, indicates. Thus, at least some specific neural mechanisms (in this case, probably the crossed and uncrossed disparity detectors) may be indeed linked directly to perception.
Mechanically adaptive implants fabricated with poly(2-hydroxyethyl methacrylate)-based negative photoresists