Presentation is loading. Please wait.

Presentation is loading. Please wait.

Vision after complete blindness: Mike May Fine et al., Nature Neuroscience 2003; Robert Kurzon, ‘Crashing Through’

Similar presentations


Presentation on theme: "Vision after complete blindness: Mike May Fine et al., Nature Neuroscience 2003; Robert Kurzon, ‘Crashing Through’"— Presentation transcript:

1 Vision after complete blindness: Mike May Fine et al., Nature Neuroscience 2003; Robert Kurzon, ‘Crashing Through’

2 But understanding normal perception is the toughest and most important challenge for psychology We tend to take normal perception for granted, while finding bizarre experiences of exceptional individuals intriguing… Occasionally, though, an exceptional individual’s experience can advance our understanding of normal perception… For instance, the case of Mike May helps us not to take perception for granted

3 To what extent does visual processing rely on visual experience?

4 Ione Fine (UCSD USC)

5 Geoff Boynton (UCSD/Salk): fMRI+

6 Ione Fine (UCSD USC) Geoff Boynton (UCSD/Salk): fMRI+ Brian Wandell (Stanford) and Alex Wade, Alissa Brewer (Stanford)

7 Ione Fine (UCSD USC) Geoff Boynton (UCSD/Salk): fMRI+ Brian Wandell (Stanford) Alex Wade, Alissa Brewer (Stanford) Stuart Anstis (UCSD)

8 Subject Mike May Blinded by a chemical accident at age 3. Light sensitive (no form vision) between ages of 3-43

9 Subject Mike May Sight restored by a new procedure - Corneal epithelial stem cell replacement

10

11 Resolution 2 & 3d Form Motion Object/Face Recognition

12 Campbell & Robson (1968) Spatial frequency (cycles/degree) Sensitivity Contrast-Sensitivity Function (CSF) Resolution limit: 50cpd

13 Resolution limit < 2 cpd, despite good optics Spatial frequency (c/deg) Log sensitivity MM (Post-operatively) Normal

14 Spatial frequency (c/deg) Log sensitivity MM + 5 months MM +11 months MM +17 months MM +21 months CONTROL No improvement over time

15 MM could identify simple shapes 2D FORM

16 …but not shapes defined by illusory contours. 2D FORM

17 Mike can identify simple 2d forms (100% correct) But “constructive” 2d perception is harder MM = 80%; controls=100%, 90%, 95%) MM = 73%; controls = 80%, 85%, 100% guessing Letters recognizable

18 3D FORM Sensitive (100% correct) to occlusion …

19 Shading gave no automatic impression of depth: 3D FORM The circle was seen as a flat disc, with non-uniform surface lightness

20 “A square with lines attached” 3D FORM Fails with: Shape from Shading: Perspective:

21 Could NOT recognize a stationary cube from any angle - “square with lines” MOTION

22 Couldn’t identify STATIC cube…but with a ROTATING one, “It’s a cube! …going in …going out”

23 Could NOT recognize a stationary cube from any angle - “square with lines” MOTION

24 Could NOT recognize a stationary cube from any angle - “square with lines” YET … Can exploit motion to construct 3D structure- “it’s a cube! …moving in, moving out” MOTION

25 Could make sense of… Point-light walker Rotational Glass patterns Structure from motion (100% correct) MM = 90%; controls=95%, 80%, 85%).

26

27 Sophisticated processing of MOTION: Can see form from motion (KDE cube) Saw depth in face masks by rocking his head Could see Johansson’s walking man Can play catch Skiing: vision now helps!

28 Motion SB (Ackroyd et al) “His only signs of appreciation were to moving objects, particularly the pigeons in Trafalgar square… He clearly enjoyed … watching … the movement of other cars on the road …He spotted a speeder coming up very fast behind us” Virgil (Sacks) “when [the gorilla] finally came into the open he thought that, though it moved differently, it looked just like a large man”

29 Gender MM 70% correct control 100% Expression (happy/sad/neutral) MM 61% correct control 100% MM 25% correct control 100% Poor object & face identification

30 Clinton&Gore By Sinha &Poggio

31

32 These dissociations between form and motion tasks were consistent with the size and activation of visual areas measured using fMRI V1 and (especially) extrastriate areas in the temporal stream, thought to be responsible for form processing, were small and showed low activity levels. The Medial Temporal complex, thought to be responsible for motion processing, was normal in both size and activation

33 Cortical area Surface area (cm 2 ) V1 (L) V1 (R) MT+ (L) MT+ (R) control observers MM Size of V1 and MT+

34 “The eye of the artist” Matches projective shapes, not real shapes, e.g. NOT susceptible to Shepard’s illusion: Tables have the SAME projective shape, and to MM they look the same

35 “flat world” Matches projective shapes, not real shapes, e.g. NOT susceptible to Shepard’s illusion: Tables have the SAME projective shape, and to MM they look the same

36 “flat world” Matches projective shapes, not real shapes, e.g. NOT susceptible to Shepard’s illusion: Tables have the SAME projective shape, and to MM they look the same

37 “flat world” Matches projective shapes, not real shapes, e.g. NOT susceptible to Shepard’s illusion: Tables have the SAME projective shape, and to MM they look the same

38 “flat world” Matches projective shapes, not real shapes, e.g. NOT susceptible to Shepard’s illusion: Tables have the SAME projective shape, and to MM they look the same

39 “flat world” Matches projective shapes, not real shapes, e.g. NOT susceptible to Shepard’s illusion: Tables have the SAME projective shape, and to MM they look the same

40 “flat world” Matches projective shapes, not real shapes, e.g. NOT susceptible to Shepard’s illusion: Tables have the SAME projective shape, and to MM they look the same

41 “flat world” Matches projective shapes, not real shapes, e.g. NOT susceptible to Shepard’s illusion: Tables have the SAME projective shape, and to MM they look the same

42 “flat world” Matches projective shapes, not real shapes, e.g. NOT susceptible to Shepard’s illusion: Tables have the SAME projective shape, and to MM they look the same

43 Images from Ted Adelson Mike correctly sees the diamonds as similar in lightness, and responds photometrically to illumination and shadow in pictures, seeing shadows as dark things. psylux.psych.tu-dresden.de/i1/kaw/diverses%20Material/www.illusionworks.com/html/shadow.html

44 Normally sighted subjects cannot retrieve any aspect of experience that is a function of retinal illuminance or projected size. But MM has these (and nothing else) available to undirected introspection. In this sense he is free (unfortunately), of the good ‘illusions’ on which normal vision is founded. One example of resulting difficulties: Shadows at the edges of sidewalks appeared to him as black ridges that could present a potential hazard in walking Phenomenal Regression to the Real Object

45 Why can’t we see and judge what’s present at the sensory input, as MM can? William James wrote: “Pure sensations can only be realised in the earliest days of life. They are all but impossible to adults with memories and stores of association acquired." For MM (though NOT necessarily for a newborn: Granrud), James may be right, perhaps because the irrepressible interpretative processes of the normally sighted brain are not involved. For the normally sighted, interpretation is not an integument that can be peeled away to reveal sensory bedrock: it penetrates all our consciousness, presumably thanks to the continuously bidirectional flow of information through the visual system. So we have no ‘pure sensations’…but those ares all that MM has. Phenomenal Regression to the Real Object

46 V1 LGN Parietal (action) temporal (perception) The visual process as a causal chain

47 V1 LGN Parietal (action) temporal (perception) In the normal visual system, each neural representation depends on the later ones. The visual process as a feedback system

48 MM was not sensitive to perspective cues DEPTH Yet he WAS susceptible to the Muller- Lyer and related illusions

49 Richard Gregory

50 “Dumbbell” variant of the Muller-Lyer illusion

51 Aesthetics Color –Variety and vividness were new and impressive Bodies –Innate sign stimuli vs. interest based on association Dust, waves, fireworks –Meaning confers no aesthetic advantage

52 Key points about Mike’s perception Mike has a severe neural resolution loss, improving slowly if at all. He doesn’t see 2D subjective contours. 2D Geometrical illusions are present. Both perspective and shape from shading are ineffective for depth perception. But motion cues are effective. Recognizing faces and common objects is a challenge. We think of Mike as having “the eye of the artist”, inhabiting a world of abstract 2-dimensional shapes and colors. This may be why he now uses his vision, as he puts it, “mainly forentertainment”

53

54 The End


Download ppt "Vision after complete blindness: Mike May Fine et al., Nature Neuroscience 2003; Robert Kurzon, ‘Crashing Through’"

Similar presentations


Ads by Google