and intensively they are (1) homonomous, (2) heteronomous. Sub-forms of both the latter types are the (in algebraic sense) positive and negative after-sensations. This use of 'positive' and 'negative' is certainly correct; but the words are already employed, in psychological optics, in two different senses, and it seems unnecessary to add a third. The temporal division is one which, at least in optics, it will be difficult to carry through.
Stimuli are classified as immediate (induction current), mediate (light- and sound-waves) and — both (mechanical, thermal, electrical). Here again the reader is, I think, rendered a little impatient by the novel terminology; so very little is won by it.
The doctrine of specific energies — which culminated in Donders' phrase, that by exchange of nerves we should hear the lightning and see the thunder — is discussed at length. The specific energy of a nerve is its capacity of definite reaction to any kind of stimulus. Dr. Dessoir weighs the facts alleged in all sense-departments,[1] and finds them wanting. But, besides the lack of supporting facts, there is a series of theoretical objections to the doctrine; and the authors of these (Helmholtz, Wundt,[2] Stumpf) are passed in review. As regards the seat of the determination of sensation-quality, a position is taken up which pretty closely resembles that of Wundt. The author concludes, with commendable carefulness, as follows: Every sense-apparatus has a specific excitation, every cortical area a specific function. Even this leaves the question open: How many of each are there?
Perceptions are in certain cases externalized (thunder-clap) and excentrically projected (contact-sensations). The key to these phenomena is given by introspection and dynamometry. Sensations are externalized when they are attended by insignificant (locally limited) muscular work; projected when they greatly (widely) strengthen the muscular force. There has been a tendency of late to apotheosize the muscle-sense; and I confess myself a sceptic. Has the attendant phenomenon
- ↑ Dr. Dessoir's objections to a periodicity-theory of color-vision do not seem well grounded. Such a theory does take cognizance of the anatomical structure of the retina (Kirschmann, in Phil. Stud., v, 493), and does recognize complementariness. For the rest, such phenomena as that described by Hilbert (Zeitschr. f. Psych, u. Phys. d. Sinnesorgane, iv, 74, ff.) accord better with a hypothesis of this type than with the others. As regards smell and taste, mechanical stimulation has been found effective by some observers; cf. Hermann's Handbuch, iii, 2, pp. 188, 189 and 256, 257.
- ↑ The writer (quoting Munk) appears to assume that a secreting cell is adequate to functions which differ as widely as perception of light from that of touch. And the first part of Wundt's argument is hardly correctly represented; see Phys. Psych., i, 337. Again (p. 217), it is only so far as it is unstable (indefinite, i.e.) that the excitation of a nervous structure can, on Wundt's view, occasion different kinds of sensations. Lastly (p. 219), has the comparison of disparate sensations much sense?
