Spatial cognitionLavanya SharanApril 11th, 2011

Measuring distance: Under constrained?

Berkeley observed that distance information is lost during retinal projection, thus visual cues are not sufficient

(Proffit 2006).

Measuring distance: Not so constrained

Gibson and Sedgwick noted that visual cues can provide relative depth information (Proffit 2006)

Many cues for distance perception

Occlusions provide ordinal distance information.

(Images: Cutting & Vishton 1995, etsy.com)

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)

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)

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)

Many cues for distance perception

Observers’ movements through a rigid, mostly planar environment can provide depth information.

(Images: Cutting & Vishton 1995, Proffit 2006)

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)

Many cues for distance perception

The input to two eyes provides stereo and therefore, depth information.

(Images: Cutting & Vishton 1995, okaygeek.com)

Many cues for distance perception

Motion perspective

Texture gradient

Binocular disparity

Accommodation

Height in visual field

Occlusion Relative sizeAerial

perspective

Why so many? How do they interact?

Cutting & Vishton (1995)

Redundancy is useful. Different cues are effective in different

ranges.

Measuring distance perception

Verbal reports

Visually directed actions

Images: dwellingintheword.wordpress.com, VPfaCGP Fig 13.2, Loomis & Philbeck 2008

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.

Klatzky et al. (1990)

However, return-to-origin tasks are hard.

Distance perception: “veridical” or not?

Veridicality means:

• Linear relationship between perceived & physical distance.• Perceptual equality of equal physical intervals.

Distance perception: “veridical” or not?

(Loomis & Philbeck, 2008)

Verbal reports Blind walking

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)

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)

Beyond distance perception: mental imagery

Roger Shepard (from intropsych.com)

Linear increase in response time with increasing rotation

Parsons (1994)

Body schema and mental imagery

Response time correlated with time to taken to attain pose

Zacks et al. (1992)

The task matters for mental imagery.

Same/different figure vs. left/right hand extendedLinear increase vs. flat response time

Is this evidence for object-based vs. viewer-based transformations?

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!