CENTRAL MECHANISMS OF VISION 



739 



creased their amplitudes. The spectral composition of 

 the stimulus affected shape, amplitude and latency. 

 The two components of the positive response were 

 most marked in response to 575 and 620 m|i stimuli. 

 The amplitude of the cortical response to the 445 m/j 

 stimulus was greater than to the 560 m/i stimulus 

 when in the retina the two were the same. The la- 

 tency of the cortical response to the 445 m/j stimulus 

 was longer than for the greater wavelength when 

 under the same circumstances the latencies were the 

 same at the retina. The final conclusion was to the 

 effect that variation in the cortical responses were not 

 solely determined at the periphery. 



The same two authors, Madsen & Lennox (54), 

 studied cortical response to spectral stimuli still fur- 

 ther. In this Study, the anterior, mid and posterior 

 optic cortices were compared by means of simulta- 

 neous recording. The double positive on-response 

 mentioned earlier was found in the posterior and mid 

 cortex. The response from the anterior cortex was 

 single. The maximum of the wave corresponded to 

 the latency of the second peak of the double waves 

 found in mid cortex within a value of from 2 to 5 

 msec. Latencies on the anterior cortex were signifi- 

 cantly longer than in posterior cortex, and the rate of 

 reduction in latency with increase in intensity was 

 more rapid. The authors attributed the difference in 

 latency between the anterior and posterior cortex to 

 the absence of the first positive peak of the on-re- 

 sponse in the anterior cortex. 



The latency of responses to the 445 m/i stimulus 

 was shorter at the anterior position and that for red 

 was longer than at the posterior position. The ampli- 

 tude for the cortical response to the 445 m/z stimulus 

 was relatively greater at the anterior than at the 

 posterior cortical position. 



The types of cortical respon.ses obtained by these 

 authors indicates that the cortex of the cat does re- 

 spond differentially to spectral stimulation. In direct 

 contrast to this, we have recent evidence for thinking 

 that the o\er-all response of the cat (its overt beha- 

 vior) does not utilize the differentials of cortical 

 response just described. Meyer et al. (58) were unaijle 

 to condition the cat differentially to the photic radia- 

 tion passed by three Wratten filters (23A, 'red'), (47, 

 'blue') and (61, 'green'). One thousand trials were 

 used for each of the comparisons of filter 23A with 

 61, and 47 with 61. As a check, a pure intensity 

 comparison was used and conditioning was accom- 

 plished in 200 trials. This led the authors to believe 

 that the cat does not possess color vision. 



The fact that differential cortical responses to spec- 

 tral stimulation can be detected and yet the same spe- 

 cies cannot be taught to respond differentially in its 

 overt behavior is a concrete example of the principle 

 which we stated earlier in this section. It is an exam- 

 ple of why we need to be quite definitive in what we 

 mean when we use the term color vision. 



To clarify matters, one had better never speak of 

 color vision in subhuman species. If the animals in 

 question can be trained to respond differentially to 

 various parts of the spectrum, we can call the beha- 

 vior overt spectral vision. Color vision is a term that 

 should be reserved for the description of human ex- 

 perience. If neurophysiological experiments indicate 

 differential response to the spectrum by any or all 

 sense cells, then it should simply be called spectral 

 response. Vision is not a term to apply to sense cell 

 behavior. Thus we have three categories of behavior 

 to talk about, spectral response, spectral vision and 

 color vision, and it is in the interests of clarity that we 

 use three terms. 



REFERENCES 



1. Adri.'\n, E. C. and G. Moruzzi. J. Fhisinl. 97: 153, 1939. 



2. B.\RTLEv, S. H. Am. J. Phsiiil. 108: 387, 1934. 



3. Hartley, S. H. Am. J. Physinl. iio: 666, 1935. 



4. Bartlev, S. H. J. Cell. & Comp. Physiol. 8: 41, 1936. 



5. Bartlev, S. H. Am. J. Physiol. 117; 338, 1936. 



6. Bartlev, S. H. Proc. Soc. Exper. Biol. & Med. 38: 535, 1938. 



7. Bartlev, S. H. Psychol. Rev. 46: 337, 1939. 



8. Bartlev, S. H. J. Exper. Psychol. 25: 462, 1939. 



9. Bartlev, S. H. J. Exper. Psychol. 27; 624, 1940. 



10. Hartley, S. H. J. Exper. Psychol. 32: 110, 1943. 



11. Hartley, S. H. J. Psychol. 32: 47, 1951. 



12. Hartley, S. H. J. Psychol. 32: 217, 1951. 



13. Hartley, S. H. J. Psychol. 34: 165, 1952. 



14. Hartley, S. H. a.nd G. H. Bishop. .Am. J. Physiol. 103: 

 159. '933- 



15. Bartlev, S. H., J. 0'Le.'\rv and G. H. Bishop. Am. J. 

 Physiol. 120:604, '937- 



16. Hartley, S. H., G. Paczewitz and E. Valsl J. Psychol. 

 In press. 



17. Hartley, S. H. and F. R. Wilkinson. J. Psychol. 33: 301, 



195^- 



18. Bishop, G. H. .Am. J. Physiol. 103: 213, 1933. 



19. Bishop, G. H. .\nd M. Clare. J. .\europhyswl. 14: 497, 



1951- 



20. Bishop, G. H. and M. H. Cl.\re. J. .\europhysiol. 15: 201, 



i95'^- 



21. Bishop, G. H. and M. H. Clare. Eleclroencephalog. & Clin. 

 .Kemophysiol. 4: 321, 1952. 



22. Bishop, G. H. and M. H. Clare. J. .Veurophysiol. 16: 1, 

 1953- 



