146 



NATURE 



[June 



process. This, too, though it would exclude such a 

 " physiological psychology " as that of Ladd, seems a 

 reasonable way of viewing the matter. Further, the 

 author proceeds to set forth the typical form of psycho- 

 physical process as reflex, and he considers that every 

 known development of the psychical phase must be 

 capable of being viewed as an incident in such a reflex 

 process. Here Dr. Ziehen meets the real difficulty in 

 psychology, and, as we see, meets it boldly. From the 

 physiological point of view we are bound to take the reflex 

 as our starting-point, and to view the most intricate 

 plexus of cerebral processes as merely an expansion of i 

 the intermediate central stage of this reflex. But can the 

 same mode of treatment be applied to the intricate inter- 

 weavings which constitute our mental life? As mere 

 events in time^ synchronizing with neural events, they 

 appear to be susceptible of being thus regarded, and this, 

 as the author rightly contends, is precisely the way in 

 which the physiological psychologist has to conceive of 1 

 psychical phenomena. 



Starting, then, with the reflex, of which the writer gives | 

 an admirable account by way of introduction, he proceeds 

 to deal with the psychical process in its three successive 

 stages, viz. sensation, answex'ing to the afferent or sensory 

 section of the nervous process ; ideation, or, as he puts it, 

 association, answering to the expanded form of the 

 central section ; and action, answering to the efferent or 

 motor section. The account of sensation is fairly full, 

 and up to date. Perhaps the treatment of the relation of 

 stimulus to sensation (Weber's law) is proportionately 

 too long. The discussion of the interpretation of the facts 

 is original and interesting. The author does not, like 

 most recent physiologists, view the logarithmic ratio of 

 stimulus to sensation as a purely physiological relation, 

 due to what Mr. James has recently called the friction of the 

 nerve-machine, but connects it with a more general psycho- 

 physical law formulated by Hering, viz. " that the purity, 

 distinctness, or clearness of a sensation or idea depends 

 on the relation in which the weight of the same, i.e. the 

 magnitude of the corresponding psycho-physical process, 

 stands to the collective weight of all simultaneously pre- 

 sent sensations and ideas, i.e. to the sum of the magnitudes 

 of all the corresponding psycho-physical processes." At 

 the same time the author is far from clear when he speaks 

 of the conscious comparison of intensities as an "asso- 

 ciative activity." This is an example of a tendency among 

 the younger physiological psychologists to force psychical 

 processes into a physiological framework. Comparison 

 cannot, as Miinsterberg's ingenious but futile attempts 

 plainly show, be regarded as merely an associative process, 

 though of course it depends on association, and in this 

 way can be correlated with a nervous process. It must, 

 however, be said in justice to Dr. Ziehen, that he is com- 

 mendably free from the common tendency of physiologists 

 to ignore psychical distinctions. Thus it is quite refresh- 

 ing to find a physiologist contending that black and grey 

 are positive sensations, having each its distinctive quality, 

 like white or blue. It may be added that special interest 

 is given to the exposition of sensation, as of the other 

 psychical phenomena, by the frequent bringing in of 

 the biological point of view, and the suggestion how, by 

 the process of natural selection, particular psycho-physical 

 NO. I 1 29, VOL. 44] 



arrangements have been brought about and rendered 

 permanent. 



The account of sensation is supplemented by a chapter 

 on the aff"ective or emotional tone of sensations, i.e. their 

 pleasurable or painful aspect. Here, again, we have 

 frequent references to the Darwinian theory, as when it 

 is suggested, d propos of the fact that extreme intensities 

 of skin-sensation, pressure, heat and cold, lose their dis- 

 tinctive sensational quality, and become purely affective 

 phenomena or pains, that this arrangement has come 

 about owing to the circumstance that in the evolution of 

 the zoological series " intensive mechanical and caloric 

 stimuli constitute the earliest, the most frequent, the most 

 direct, and the greatest danger to the animal organism " 

 (p. 85). The author refers the whole of the difference 

 in affective tone among colours, and among combinations 

 of musical sound, to association. This seems to be 

 going too far. The contrast between the exhilarating 

 effect of the warm colours, and the quiet effect of those at 

 the violet end of the spectrum, seems to be connected 

 in part with the difference in the underlying nervous 

 processes ; and this is certainly true, as Helmholtz has 

 shown, with respect to the emotional aspect of certain 

 accords, e.g. the major and minor triads. 

 . Coming now to the account of the idea (image and 

 concept), we note that Dr. Ziehen differs from the majority 

 of contemporary psychologists in assigning a separate 

 cortical element to the sensation and to the idea. These 

 different cells (the author, in spite of Lewes's attacks on 

 the cell-superstition, talks of the individual cell as the 

 seat of a sensation) are closely connected, and in this 

 way the after-effect of sensations in memory, as also the 

 reflex effects of ideas in exciting sensations, as in hallu- 

 cinations, are accounted for. The writer elaborates his 

 peculiar anatomical hypothesis in an ingenious way. He 

 seems to admit, however, that it is a pure hypothesis, 

 for the facts of ''mental blindness" referred to are not 

 apparently put forward as a proof ; and it may be added 

 that rightly viewed they do not seem even to suggest the 

 hypothesis. One may add that it appears to lack the 

 only possible justification of such a hypothesis, viz. that 

 it simplifies the interpretation of the facts. The other 

 supposition, that the sensation and the idea involve the 

 same group of central elements (not the same single cell), 

 is more reasonable in itself, and seems to off"er a readier 

 explanation of most of the phenomena. 



The account of the psycho-physical process in asso- 

 ciation is less clear and instructive than most of the 

 exposition. The author follows Miinsterberg a good way 

 at least — in reducing all association to one form, viz. con- 

 tiguous, and more particularly simultaneous, association. 

 But the diagrammatic representation of the processes 

 strikes one as needlessly complicated by the hypothesis 

 of separate ideational nerve-cells. Much better is the 

 account at the close of this lecture of the way in which 

 the different psycho-physical factors co-operate and 

 modify one another in the actual concrete processes of 

 reproduction. Dr. Ziehen is particularly happy in ex- 

 plaining the great variability of the sequences of our ideas 

 from moment to moment. The account of the ideational 

 stage is completed by a discussion of the relation of 

 association to judgment and reasoning — which is a little 



