642 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY I 



identical with, consciousness. Identification marks and 

 courtship gestures are significant in these terms. In- 

 sects which go habitually from one flower to another 

 of the same kind demonstrate this type of discrimina- 

 tion; efficient pollination often depends upon it. 



To be useful in form perception and pattern recog- 

 nition, a photosensory mechanism must carry inten- 

 sity discrimination the further step of detecting simul- 

 taneously in small areas of the visible field the 

 differences in intensity which are significant. Several 

 types of acuities are involved, all of them properly 

 defined as the reciprocals of threshold intensities, 

 whether linear, areal or angular. How large must a 

 single object be to constitute an adequate stimulus? 

 How far apart must two objects be for the gap be- 

 tween them to be visible? Can an object, such as a 

 triangle, be significant in one orientation (say up- 

 right) but not another (say inverted}? Is alignment, 

 or motion or distance significant to the organism as it 

 views objects in the environment? 



The camera-style eye and the compound eye appear 

 most competent to interpret the world in terms of 

 small differences in light intensity and to send mes- 

 sages to the central nervous system from which a 

 picture of the environment can be assembled. Even 

 for organisms with these eye types, pessimistic views 

 have often been expressed. Frequently they represent 

 inadequacy of experimental technique. "Absence of 

 evidence is no evidence of absence." Thus VVillem 



(295) concluded terrestrial mollusks could detect the 

 presence of voluminous objects only when less than a 

 centimeter distant, but \on Buddenbrock (269) re- 

 ported compensatory movements of the eyestalks to a 

 rotating visual field much farther away. And various 

 workers (100, 258) have had difficulty satisfying 

 themselves that cephalopod mollusks respond to visual 

 cues in the absence of simultaneous tactile and gusta- 

 tory stimulation. 



Plateau (217) obtained so few responses to the 

 stimuli he gave to captive spiders that he concluded 

 that they were essentially blind. Apparently some ob- 

 jects are recognized and others ignored, so that the 

 acuities possible are not always demonstrated (208). 

 No doubt Mallock (i 78) gave far too optimistic values 

 of resolution in spider ocelli since he used the out- 

 moded Rayleigh criterion in his calculations. Ho- 

 mann's estimates (127-129) correspond more closely 

 with observed reactions. 



In.sect behavior seems to match reasonably well 

 with predictions based on measurement of eyes and 

 binocular fields (29, 47, 172, 173, 250, 307). Lack of 

 accommodation — an ability claimed for ommatidia 

 only once (265) — is of no significance in an apposition 

 eye since no image is formed (256), or in a superposi- 

 tion eye since image resolution has been sacrificed for 

 increa.sed sensitivity. The mosaic style of vision tends 

 to stress the importance of movement and find detail 

 only at very close range. 



REFERENCES 



1. Abbott, C. E. Tuiiox .News 27: 138, 1949. 



2. Alexandrowicz, J. S. Arch. zool. exper. et gen. 66: 71, 1927. 



3. Andrews, E. A. J. Morphol. 5: 271, 1892. 



4. Arey, L. B. J. Comp. Neurol. 26: 359, 191 6. 



5. Arey, L. B. and W. J. Crozier. J. Exper. ^ool. 32: 443, 

 1921. 



6. AuTRUM, H. Experienlia 5: 271, 1949. 



7. AuTRUM, H. AND N. Stocker. Bwl . ^enlialbl. 71: 129, 

 1952- 



8. Baldus, K. .^Isikr. vergleich. Pliysiol. 3: 475, 1926. 



9. Bauers, C. Z^schr. vergleich. Physiol. 34: 589, 1953. 



10. Baumgardt, E. L. M. J. Gen. Physiol. 31: 269, 1948. 



11. Baumgartner, H. ^Ischr. vergleich. Physiol. 7: 56, 1928. 



12. Baylor, E. R. and F. E. Smith. Am. Natural. 87: 97, 1953. 



13. Beddard, F. E. Voyage of H. M. S. Challenger, ^oot. 11(3, 

 Part 33): I, 1884. 



14. Belehradek, J. and J. S. Huxley. J. Exper. Biol. 7: 



37. 1930- 



15. Bennitt, R. J. Exper. ^ool. 40; 381, 1924. 



16. Bernard, F. Bull. biol. France Belg. Suppl. 23: i, 1937. 



17. Bertholf, L. M. J. Econ. Entomol. 20: 521, 1927. 



18. Bertholf, L. M. J. Agr. Res. 43: 703, 1931. 



19. Beuther, E. Silzber. .ihhandl. nalurforsch. Ges. Roslock I : 

 I, 1926. 



20. Bliss, A. F. J. Gen. Physiol. 26: 361, 1943. 



21. Bliss, .\. F. Biol. Bull. 91: 220, 1946. 



22. BoLWiG, N. V'tdensk. .Meddelelser Dansk nalurhisl. Foren. 

 h oebenhavn i og : 80, 1 946. 



23. Bozler, E. ^Ischr. vergleich. Physiol. 3: 145, 1925. 



24. Brand, H. ^Ischr. wiss. ^ool. 144: 363, 1933. 



25. Brecher, G. y^tschr. vergleich. Physiol. 10: 497, 1929. 



26. Brues, C. T. Proc. Am. Acad. Arts Sc. 74: 281, 1941. 



27. Brunotte, C. Compt. rend. Acad. Sc, Paris 106: 301, 1888. 



28. Buck, J. B. Physiol, ^ool. 10: 45, 1937. 



29. Burt, E. T. and W. T. Catton. Nature, London 170: 285, 



'95^- 



30. Carriere, J. Qjiart. J. Microsc. Sc. 24: 673, 1884. 



31. Carriere, J. Die Sehorgane der Thierc. Munich: Olten- 

 bouig, 1885. 



32. Causey, N. B. Turtox News 33: 200, 1955. 



33. Chun, C. Verhandl. deutsch. zool. Gesellsch. 13: 67, 1903. 



34. Collins, D. L. and \V. Maciiado. J. Econ. Entomol. 28: 



'03. 1935- 



35. CoNST.ANTiNEANU, M. J. ^ool . Jalirb., .ibt. Anat. Ontog. 



Tiere 52: 253, 1930. 



36. Corneli, W. .^ool. Jahrb., .iht. .-inat. Ontog. Tiere 46: 



573. '924- 



37. CowLES, R. p. J. Exper. ^ool. 9: 387, 1910. 



