1. VISUAL SPACE ANISOTROPY IN FULL-CUE AND REDUCED-CUE CONDITIONS Oliver Tošković Faculty of Philosophy, Kosovska Mitrovica; Laboratory for Experimental Psychology, Belgrade, Serbia

2. VISUAL SPACE GEOMETRY  Blumenfeld and Hillebrand: parallel alleys lie inside distance alleys

3. VISUAL SPACE GEOMETRY  Luneburg – perceived space is Riemannian space (with constant Gaussian curvature) Points on a Vieth-Müller circle are being perceived as equidistant from the observer Hyperbolae of Hillebrand are being perceived as radial lines of constant direction LDy x

4. VISUAL SPACE GEOMETRY  Luneburg – perceived space is Riemannian space (with constant Gaussian curvature) Points on a Vieth-Müller circle are being perceived as equidistant from the observer Hyperbolae of Hillebrand are being perceived as radial lines of constant direction LDy x

5. VISUAL SPACE GEOMETRY  Luneburg – perceived space is Riemannian space (with constant Gaussian curvature) Points on a Vieth-Müller circle are being perceived as equidistant from the observer Hyperbolae of Hillebrand are being perceived as radial lines of constant direction LDy x

6. PHYSICAL vs PERCEIVED SPACE  Herman von Helmoltz: Difference between physical and perceived horopter Change in perceived horopter with distance L R horopter

7. PHYSICAL vs PERCEIVED SPACE distance perception perception of parallelism observer  Koenderink, J. Cuijpers, R.

8. MOON ILLUSION  Ptolemy – apparent distance  Alhazen – moon illusion as a psychological phenomenon  Rock and Kaufman –apparent distance theory –flattened sky dome physical dome perceived dome

9.  Tošković (2004) distance perception  Elliptic model of visual space (anisotropy) Phisically shorter vertical distances = longer horizontal Vertical distances are peceived as beeing longer

10. Rock and Kaufman

11. standinglying eyes body head physical distance perceived distance perceived- physical size deviation  Tošković (2007) For near distances, such as 1m, visual space is isotropic For larger distances (3m and larger) visual space is anisotropic  For distance estimates, visual system uses additional information from: Vestibular system Neck muscles

12. TO RESUME:  In a reduced cue-situation: For perceived distance, visual space is anisotropic It relies on additional vestibular and kinesthetic information Anisotropy – an internal model of visual space  In a full-cue situation: ?

13. AIM  Does visual space anisotropy exist in full cue situation, as in reduced cue situation?  Does kinesthetic information influence distance perception in full cue situation, as in reduced cue situation?  Does visual system relie on its internal model of space even when visual information are present?

14. METHOD  Two experiments were conducted, with participants lying on their left side of the body Head moving does not change vestibular information Uniform distribution of depth cues in all directions  Sample: 37 psychology undergraduates and high school students  Stimuli: three luminous objects rectangular in shape size: 7* 5 centimeters

15. EXPERIMENT 1: reduced-cue  Sample: 13 psychology undergraduates  Procedure: Participants estimated distances  In a dark room – reduced cue situation  Lying on a floor, on left side of the body  With special glasses on their eyes (with horizontal apertures 1mm wide)  With rectangular frame around their head Three standard distances to estimate - 1, 3 i 5 meters Three directions of estimate  horizontal (0 0 )  middle – tilted for 45 0 regarding to horizon  vertical (90 0 ) Task – equalize the distances of three stimuli on a three different directions

16. stimuli glasses frame

17. RESULTS  DIRECTION: horizontal – middle NO significant effect of direction NO interaction between direction and distance  DIRECTION: horizontal – vertical Significant effect of direction Significant interaction between direction and distance  DIRECTION: middle – vertical Significant effect of direction Significant interaction between direction and distance

19.  Visual space is being ELONGATED towards vertical direction For the distances larger than 1m Effect is NOT measurable on 45 o tilt from horizontal direction  In a reduced-cue situation visual space is anisotropic: neck muscles information influence distance perception

20. EXPERIMENT 2: full-cue  Sample: 24 high school students  Procedure: Participants estimated distances  On an open field – full cue situation  Lying on a ground, on left side of the body  With special glasses on their eyes (with horizontal apertures 1mm wide)  With rectangular frame around their head Three standard distances to estimate - 1, 3 i 5 meters Three directions of estimate  horizontal (0 0 )  middle – tilted for 45 0 regarding to horizon  vertical (90 0 ) Task – equalize the distances of three stimuli on a three different directions

21. stimuli glasses frame

22. RESULTS  DIRECTION: horizontal – middle No effect of direction No interaction between direction and distance  DIRECTION: horizontal – vertical NO effect of direction No interaction between direction and distance  DIRECTION: middle – vertical NO effect of direction No interaction between direction and distance

24.  Visual space is NOT being ELONGATED towards vertical direction Perceived distance does not change with viewing direction  In a full-cue situation visual space is isotropic: neck muscles information does NOT influence distance perception

25. CONCLUSIONS  In a reduced-cue situation: For near distances, such as 1m, visual space is isotropic For larger distances (3m and larger) head tilt ELONGATES space towards vertical direction visual system uses additional kinesthetic information from neck muscles  In a full-cue situation: For all distances visual space is isotropic Head tilt does not change visual space towards vertical direction visual system does NOT use additional kinesthetic information from neck muscles  Presence of visual information reduces significance of kinesthetic (non-visual) information for distance perception