2. Introduction Key point: motion perception can be dissociated from normal vision Participants: WW1 officers with gunshot wounds (invariably injured ‘while advancing’ despite shot in the back of the head), which caused scotomas Visual fields mapped with peripheral discs. Patient self-reports when perceived (n.b., no force-choice method necessary). Also tests with moving or static fingers. Residual motion perception is vague and shadowy, without shape or colour recognition

3. Group 1 - Motion perception only Patients perceive finger movements, but not static fingers Motion perception sometimes not present initially - recovers, seemingly without practice, starting in periphery In these cases, no complete recovery of motion perception occurs e.g., case 1: Bullet wound to right occipital lobe Perceives motion normally throughout visual fields, despite left hemianopia Motion perceived as ‘shadowy grey’ No improvement 6 months later

4. Group 2 – Showing Recovery of both Perceptions 4/10 cases The recovery of vision for movement precedes that for objects Recovery is greater for movement than for object Recovery of movement vision begins in the peripheral field Dissociation between movement and object vision Red = Movement Green = Object

5. Group 3 – Where no dissociation or recovery of vision occurs. Case 10 - received a bullet to the left occipital region. Developed right hemianopia. Showed no dissociation between object and movement vision. Records of his visual field taken at intervals for seven months. No change after 8 months.

6. Conclusion The appreciation of movement in the so-called blind field is the earliest indication of recovering vision. The dissociation between movement and object recognition gives insight into whether recovery will occur. Recovery of movement begins at the periphery and extends inwards.

7. Residual Visual Function After Brain Wounds to the Central Visual Pathways in Man Poppel, Held & Frost (1973). Rachel Foxwell, Alice Curling,Erika Davies, Amrita Diwanji

8. Aims It was previously believed that damage to the visual cortex would lead to complete blindness, but this was only measured in absolute terms. Using a localising response task, Poppel et al. were looking to find evidence of residual visual function after damage to the visual cortex.

9. Methods 4 participants with traumatic (3) or vascular (1) lesions to the occipital regions leading to a scotomata were tested. They had to follow a light target. The light target varied in eccentricity from the center.

10. Results Participants could not identify correct target positions. The further out the target, the farther their eyes moved. This was statistically significant.

11. Discussion There is some evidence of residual visual function in patients with visual cortex lesions. This could be due to: –The midbrain –Functioning orientating response in the visual cortex If it’s the latter, this suggests a dissociation between detection and localisation.

12. Summary of Weiskrantz et al., 1974

13. What did the study investigate? Damage to the striate cortex and residual visual function Case study of patient D.B. who had restricted lesion of the right occipital lobe

14. Experiment 1 Locating an eye fixation Method: –spot of light on blind field –Fixate eyes to where they thought the light came from

15. Results – Experiment 1

16. Experiment 2 Locating by reaching with finger Method: –Same as expt. 1, but with reaching to target –Also altered size of target

17. Results – Experiment 2

18. Experiment 3 Horizontal vs. vertical lines, diagonal vs. vertical lines and X vs. O Method: –Asked which of the pair was presented to the blind sight –Varied the size, contrast, duration or type of the stimuli

19. Results – Experiment 3 D. B. was able to guess well above chance levels provided that stimuli were above the critical size.

20. Experiment 4 Minimal separable acuity Method: –Varied spatial frequency of gratings to acquire acuity thresholds

21. Results – Experiment 4

22. Experiment 5 Red vs. green Method: –Red or green spots of light shown in blind field – had to identify the colour –Varied size of stimulus and brightness

23. Results – Experiment 5 Large bright stimulus29/30 Small bright stimulus21/30 Large dim stimulus22/30 Small dim stimulus24/30 Random brightness stimulus 19/30

24. What did the study find Even though the patient had no awareness of ‘seeing’ in his blind field, evidence was obtained that: 1.He could reach for visual stimuli with considerable accuracy 2.Could differentiate the orientation of a vertical line from a horizontal or diagonal line 3.Differentiate between X and O

25. What did the study find 4.There was a weak but significant correlation between target position and eye fixation (only out to 30 o eccentricity). 5.He could differentiate a grating of vertical bars from a homogenous field. 6.Suggestive but inconclusive evidence for an ability to differentiate between red and green.

26. Relation to animal lesion studies Pasik and Pasik (1971): Total removal of striate cortex in monkeys does not abolish pattern discrimination. Although they are slower to learn such discriminations. It has been speculated that the residual vision of a monkey lacking striate cortex is essentially normal qualitatively but is amblyopic, lacking capacity to discriminate fine detail.

27. Main point The observations suggest that the visual capacity remaining after damage to striate cortex may be much greater than is commonly accepted.

28. Summary of Blythe et al 1986 Presented by Shan Huang, Gina Humphreys, Charlotte James, Caroline Jennings, Alister McCormick Seminar Topic:Blindsight Date:17 th January 2008

29. What question did the study answer? Show evidence for the response to bright, transient lights presented in the ‘blind’ visual areas –sensation of a ‘dark shadow’ vs. blindsight Show how this relates to the conscious detection of stimuli Whether there are two separate pathways for visual systems

30. How did the study answer the question? Measurements made monoptically with the right eye. Stimuli = two circular spots of equal luminance but varying in distance apart which were presented sequentially. Distance btwn and order of sequence randomly varied btwn presentations. Also tested for ability to differentiate btwn seeing 1 or 2 targets, identify geometrical patterns or targets of different shapes or sizes and distinguish btwn gratings and a uniform field of illumination.

31. What did the study find? As the displacement (d) between dots increases, the probability (p) of correctly identifying the direction of movement increases rapidly. Similar pattern of results for “blind” (figure a) and non- blind subject (figure b), but blind subject shows slightly lower discrimination for displacement.

32. How do the results relate to other work? Results support previous research on ablation studies in non-human animals (e.g. Schneider, 1969). Suggests that visual function is served by two different pathways: –Evidence of a complete functional dissociation between visual localisation and pattern discrimination.

33. Summary of the main points Considers damage to the striate cortex in relation to the “two systems theory” of visual organization. Case studies. Detection/identification of light stimuli presented to “blind” visual field. Near normal ability to discriminate target displacements. Unable to discriminate spatial pattern or size. Results consistent “two systems theory”.

34. Wavelength sensitivity in blindsight Stoerig & Cowey (1989)

35. Introduction Previous research has shown that lesions in V1 does not lead to total blindness, but some visual functioning remains (movement, flicker and orientation). Colour discrimination is controversial.

36. Question Can the pathways from the degenerated hemiretina process wavelength information?

37. Method They measured spectral sensitivity in the normal and blind fields of 3 blindsighted patients and 2 normal observers.

38. Method 2 Adaptation to both light and dark was used using monocular viewing. The field defect was on the temporal side of the brain which corresponds to the more sensitive nasal retina. Nine colour targets from 450 to 600nm were used. The stimulus intensity was increased until the subject reported seeing it on 3 consecutive presentations. For the blind field, a guessing paradigm was used.

39. Under scotopic conditions  thresholds were determined by presentation of the targets in the natural blind spots. Under photopic conditions  targets could NOT be made intense enough to become detectable in the blind spot.

40. Results

41. Our interpretation

42. As shown by the spectral sensitivity curve Dark Adaptation: Sensitivity in both normal and blind fields has a single peak at 500nm under the smooth curve and a steep decline above 550nm  Characteristic of rod vision. Decreased sensitivity of the luminance system towards the shorter wavelengths because of no input from short (blue) cones, indicates that colour-opponent processes contribute to determine thresholds for the blue stimulus. Moreover, results of colour naming at threshold in the good field was faultless for the blue and red, but uncertain and occasionally wrong for green and yellow stimuli.

43. ..continued Sensitivity in blind fields is normal (except reduced by one log unit and curve less smooth). Therefore, not based on the detection of light scattered onto the functionally normal retina.

44. Light Adaptation: There is no steep decline in sensitivity above 550nm; instead the curve shifts to longer wavelengths. Therefore, cones are involved.

45. Conclusion Spectral sensitivity differs between normal and cortically blind hemifields only in terms of absolute sensitivity (fairly small difference, as shown in the graph). This difference is NOT an artefact of comparing different detection methods (not altered by guessing paradigm). No evidence that sensitivity is mediated exclusively by rod receptors (difference between dark and light). All measurements from photopic conditions show contributions from cone receptors.

46. Evidence that surviving Pβ ganglion cells, the only ones known to provide colour-opponent signals, are still functional. Therefore, remaining retinal projections to the thalamus and from there to extrastriate cortex may be involved.

47. Question Can the pathways from the degenerated hemiretina process wavelength information? YES!

48. Wavelength Discrimination in Blindsight Stoerig & Cowey (1992)

49. Introduction Damage to the V1 causes retrograde degeneration in the corresponding parts of the dLGN and the retinal ganglion cell layer The transneuronal degeneration in the retina selectively affects the P/3 (primate beta) ganglion cells that project to the parvocellular portion of the dLGN and provide the retinal input for the colour- opponent channels unidentified secondary pathways with colour- opponent wavelength processing may exist. –a subpopulation of P/3 cells escapes degeneration Behavioural evidence comes from studies of residual visual functions in the homonymous visual field defects produced by the lesions.-- 'blindsight'

50. Introduction The few studies of residual wavelength processing in blindsight are interesting in view of possible colour- opponent pathways to targets other than the striate cortex. –E.g. Using forced-choice paradigm, Stoerig (1987) demonstrated red-green discrimination in six out of 10 patients The problem with investigations of wavelength discrimination in blind fields is to eliminate clues from subjective differences in the brightness of the stimuli. Thus luminous efficiency of coloured stimuli were matched on the basis of previous measurements of the same patients' increment-threshold spectral sensitivity curves. – measured on a white adapting background with large, long stimuli to facilitate the colour-opponent system –showed the characteristic discontinuities that indicate a contribution from colour-opponent channels.

51. Introduction Aim: To see whether the patients would then also be able to discriminate between paired coloured stimuli matched for their luminous efficiency on the basis of these curves

52. Method 3 patients – P1, P2, P3 All had vascular lesions in the posterior cerebral artery Tested eye with defect in temporal hemifield (corresponds to nasal retina) – other eye covered with an eye patch Firstly did a test on visual field to determine their blind field

53. Method Once visual field was established, presented stimuli to the areas the patients could not perceive (black areas)

54. Method Presented coloured stimuli to peripheral blind fields Colours: orange (600nm), yellow (580nm), green (553nm) Yellow-green (560nm), and yellow-orange (588nm) also tested to determine wavelength discrimination thresholds Patients consistently and repeatedly reported having no conscious visual experience of the stimuli presented to their blind field

55. Results Wavelength Discrimination Orange (600nm) vs Green (553nm) discrimination Each curve based on 1250 stimulus presentations All three participants showed statistically significant discrimination.

56. Results: Wavelength Discrimination Yellow (580nm) vs Green (553nm) discrimination Each curve based on 2500 stimulus presentations P1 and P3 performed well above chance P2 only had 1 significant ROC point and performed at chance

57. Results: Wavelength Discrimination Orange (600nm) vs Yellow (580nm) discrimination Peak transmission only 20nm apart P1 and P3 again performed well above chance Despite presence of individually significant points, P2’s ROC is not significantly different from the diagonal showing again chance performance.

58. Results: Wavelength Discrimination Summary P2’s performance deteriorated with decreasing separation in peak transmissivity. Although P(A) is not significant for P2, overall performance for the patients is best for yellow-orange discrimination.

59. Results Additional Measurements in P1 Tested on two additional stimulus pairs Red (635nm) vs Green (528nm) –Shows that an increase in wavelength separation doesn’t improve discriminability as similar result to yellow-green discrimination. Yellow (580nm) vs Bluish Green (500nm) –Matched at 0.3log units above threshold. –Shows that even with stimuli closer to detection threshold, discrimination remained significant.

60. Results:Wavelength Discrimination Thresholds Ten stimulus pairs with peak transmissions from 553nm to 600nm were used in an attempt to estimate wavelength discrimination in normal and blind hemifields Patients tested in normal nasal, normal temporal and blind temporal fields. P2 –Normal Field: Could discriminate wavelengths perfectly down to 20nm and above chance for all except a separation in wavelength of 7nm –Defect Field: Performance only significant for two of the most separated pairs P3 Normal Field: Could discriminate all but the wavelengths separated by just 7nm in the normal nasal hemifield Defect Field: Could discriminate all down to the 20nm separation No difference was observed between normal fields of patients and controls

61. Discussion Wavelength discrimination tested using stimuli matched for luminous efficiency –All 3 patients showed evidence of being able to discriminate between 2 or more stimuli at statistically significant levels However, some degree of variability.

62. Discussion Large individual differences found in discrimination ability Control condition confirmed that matching for luminous efficiency was effective

63. How is wavelength processing achieved in a field defect? Three visual subsystems Pα –Thought to play a role in motion processing (not likely to have colour-opponent properties)

64. How is wavelength processing achieved in a field defect? Pβ –Prominent colour-opponent properties –Thought to be associated with processing of spatial detail and wavelength –Trans neural retrograde degeneration of retinal ganglion layer is selective for these cells (80% destroyed) –Portion survive, could be sustained by remaining geniculate neurons –Could project somewhere else i.e. the Pulvinar

65. How is wavelength processing achieved in a field defect? Pγ –No signs of transneuronal degeneration –Project to the superior colliculus (remains functional in absence of striate cortex) –Neurons show band-pass characteristics –Insufficient to signal wavelength independently of luminous intensity But…combination of surviving Pβ projections with Pγ cell projection to the superior colliculus wavelength discrimination may be possible.