The eleventh Symposium of the International Research Group on Colour Vision Deficiencies (IRGCVD) was held 20-23 June 1991 in Sydney, Aus tralia, ably hosted by local organizer Stephen Dain. A total of 35 talks and 10 posters were presented. Papers based on 37 of these presentations are included here, in Colour Vision Deficiencies XI. The scientific program featured sessions on three special topics, with each topic highlighted by an invited speaker. The opening session on the Genetics of congenital colour vision deficiencies began with a superb invited lecture by Charles Weitz about his pioneering work on the molecular genetics of tritanopia. The session on the second special topic, Spatial aspects of colour vision, began with the launching of a new IRGCVD tradition, as 1991 Verriest Memorial Award recipient Harry Sperling presented the first Ver riest Memorial Lecture on his recent studies of spatial discrimination of heterochromatic stimuli. Dr. Sperling reported new evidence that certain asymmetries in red-green opponent colour vision can be explained by the spatial organization of colour-opponent retinal neurons. In the third special session, on Occupational aspects of colour vision, Barry Cole took the audi ence on a fascinating tour of the historical development of colour vision standards in his invited lecture entitled 'Does defective colour vision really matter?'. In addition to the three special topics, many interesting presentations were given in topical sessions on Variations in normal colour vision, Acquired colour vision deficiencies and Colour vision tests and testing methods.

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1. Studies on the molecular genetics of tritanopia (Invited Paper).- 2. Structure-function relationships in human red/green color vision.- 3. Classification of anomalous trichromatism with the Nagel anomaloscope.- 4. ERG flicker photometric evaluation of spectral sensitivity in protanopes and protanomalous trichromats.- 5. Spatial discrimination of heterochromatic stimuli: A review and a new experimental approach (Invited Paper and First Verriest Memorial Lecture).- 6. Relative contributions of luminance and chromaticity to the Craik-Cornsweet effect.- 7. Opponent-colour responses generated by spatially tuned mechanisms in human vision.- 8. Does defective colour vision really matter? (Invited Paper).- 9. The ability of colour defective observers to recognise an optimised set of red, green and white signal lights.- 10. The clinical use of the Holmes-Wright lantern.- 11. Electrophysiological estimates of individual variation in the L/M cone ratio.- 12. The visual characteristics of a case of Pigmentfarbenanomalie.- 13. Sensitivity of screening tests for S-cone discrimination.- 14. Matching range and age in a blue-green equation.- 15. The effect of tinted posterior chamber IOLs on color vision.- 16. Visual functions associated with rhesus visual pursuit tracking.- 17. Image diffusion in cataracts affects chromatic and achromatic contrast perception differently.- 18. Acute changes in blood glucose and their effects on color vision function in diabetes.- 19. Longitudinal changes of visual function over 18 months: Evaluation of eyes with high-and low-risk macular degeneration characteristics.- 20. On the assessment of visual impairment caused by Anandron: Colour discrimination versus dark adaptation.- 21. The relationship between colour vision loss, contrast sensitivity lossand aging.- 22. Alterations in morphology and ERG spectral sensitivity after near IR (1064 nm) multiple parafoveal Q-switched laser exposure.- 23. Selective loss of S-pathway sensitivity in central serous choroidopathy revealed by spatio-chromatic visual evoked cortical potentials (VECP).- 24. A new iso-value colour vision test.- 25. Clinical experience with Pflüger trident plates for testing color vision.- 26. Screening of red-green defectives with the Hahn colour vision test.- 27. Using panel tests in screening for congenital colour vision defects.- 28. Clinical evaluation of Lanthony's Tritan Album.- 29. The Farnsworth-Munsell 100-hue test in cone excitation space.- 30. S-cone discrimination sensitivity and performance on arrangement tests.- 31. New normative data for the Farnsworth-Munsell 100-hue test.- 32. Characteristics of random arrangements of the Farnsworth Panel D-15 test.- 33. Suitability of fluorescent tube light sources for the Ishihara test as determined by colorimetric methods.- 34. Design criteria for a clinical anomaloscope.- 35. Automated Rayleigh and Moreland matches: Optimization of stimulation parameters for normal observers.- 36. A filter for simulating color and spatial vision of the elderly.- 37. Evaluation of the 'Différenciateur de Tonalité': An apparatus for measuring wavelength discrimination.- 38. Aberrant flicker sensitivity revealed by heterochromatic modulation photometry.- 39. Loss of chromatic response to monochromatic increments on intense achromatic pedestal backgrounds.- 40. Linear colour mechanisms obtained from detection thresholds in cone contrast space.- 41. Characterization of colour detection channels by use of their interactions.- 42. Colour vision testing using spatiotemporal luminance masking: psychophysical andpupillometric methods.- 43. Variations in colour matching data associated with light losses in the macular pigment.- Author Index.- Symposium Proceedings List.