1. Spatial cognition Lavanya Sharan April 11th, 2011

2. Measuring distance: Under constrained? Berkeley observed that distance information is lost during retinal projection, thus visual cues are not sufficient (Proffit 2006).

3. Measuring distance: Not so constrained Gibson and Sedgwick noted that visual cues can provide relative depth information (Proffit 2006)

4. Many cues for distance perception Occlusions provide ordinal distance information. (Images: Cutting & Vishton 1995, etsy.com)

5. Many cues for distance perception Relative size can provide ordinal and scaling distance information. However, variability in sizes (~10%) makes this cue non-informative. (Images: Cutting & Vishton 1995, nysun.com)

6. Many cues for distance perception Knowing one’s own height can be useful for absolute or relative distances assuming no floating objects and opaque planar surfaces that are orthogonal to gravity. (Images: Cutting & Vishton 1995, newswritingworld.blogspot.com)

7. Many cues for distance perception Atmospheric effects can provide depth information (e.g., further objects look bluer and are decreased in contrast.) (Images: Cutting & Vishton 1995, city-data.com)

8. Many cues for distance perception Observers’ movements through a rigid, mostly planar environment can provide depth information. (Images: Cutting & Vishton 1995, Proffit 2006)

9. Many cues for distance perception To focus at different distances, our eyes accommodate by changing the focal length of our lenses. (Images: Cutting & Vishton 1995, eyepower.nl)

10. Many cues for distance perception The input to two eyes provides stereo and therefore, depth information. (Images: Cutting & Vishton 1995, okaygeek.com)

11. Many cues for distance perception Motion perspective Texture gradient Binocular disparity Accommodation Height in visual field OcclusionRelative sizeAerial perspective Why so many? How do they interact?

12. Cutting & Vishton (1995) Redundancy is useful. Different cues are effective in different ranges.

13. Measuring distance perception Verbal reports Visually directed actions Images: dwellingintheword.wordpress.com, VPfaCGP Fig 13.2, Loomis & Philbeck 2008

14. Why blind walking? Image source: napraten.nu De-emphasize visual cues. Test whether observers can dynamically update their positions. Observers are reasonably good at this task.

15. Klatzky et al. (1990) However, return-to-origin tasks are hard.

16. Distance perception: “veridical” or not? Veridicality means: Linear relationship between perceived & physical distance. Perceptual equality of equal physical intervals.

17. Distance perception: “veridical” or not? (Loomis & Philbeck, 2008) Verbal reportsBlind walking

18. Distance perception: “veridical” or not? Veridicality: Linear relationship between perceived & physical distance. Perceptual equality of equal physical intervals. (Wagner 1985, Toye 1986, Philbeck et al. 2004) Depth foreshortening (Images: tileandstonedallas.com, 123rf.com)

19. Context influences distance perception Image sources: familychiropracticcenter.wordpress.com, sportclipart.com, meagan- ryanne.blogspot.com Being tired makes distances seem further. (Proffit et al. 2003, Witt et al. 2004) Purpose of the task at hand matters. (Witt et al. 2004) Fear makes distances seem larger. (Schnall et al. 2005, Proffit 2006, Stefanucci 2006)

20. Beyond distance perception: mental imagery Roger Shepard (from intropsych.com) Linear increase in response time with increasing rotation

21. Parsons (1994) Body schema and mental imagery Response time correlated with time to taken to attain pose

22. Zacks et al. (1992) The task matters for mental imagery. Same/different figure vs. left/right hand extended Linear increase vs. flat response time Is this evidence for object-based vs. viewer-based transformations?

23. Implications for computer graphics Head mounted displays Virtual worlds (Sistine Chapel in Second Life) Images: digitalcortex.net, eternallycool.net, cbs19.tv Desktop displays Class discussion!