The moon illusion-Perception

Using after-images to highlight the size constancy

-Present image to eye and fatigue (adapt) visual receptors that are firing as a result of this image -To create an afterimage you present a high stimulation image on a low stimulation background -After-image is the opposite color of the image (reverse image) -May either be because of fatigued receptors on the retina or because your brain adapts to that and then is adapted so with the newly adapted program it suddenly sees the opposite

Human visual perception

-Perception is more than sensation (the eye provides a sloppy image and the mind changes it into a beautiful, 3D picture) -Perception is a function of top-down and bottom-up processes ---Comes into visual cortex depending on which part of the visual field it was from, but from there, the signal goes pretty much everywhere & gets more and more complex ---Most of these pathways have pathways that go back through the occipital cortex and even back to the retina ---Recurrent processing = the feedback that the visual signals send back to the occipital cortex/eye

Moon illusion

-1.5 - 2 times larger on the horizon -Not just moon - sun, planets, stars ... -Sometimes there is a 'super-illusion' >2x -First known scientific explanation Aristotle 300BC (atmospheric distortion) -Tells us that the brain got it wrong, but also helps us understand what it does when it does get it right -Real moon's size ---Moon's size corresponds to a visual angle of 0.5 degrees -Size of moon on the retina is 0.15 mm -Real size changes are opposite to the illusion (when it looks bigger, it's actually farther, when it looks smaller it's actually closer) ---Not something physical but something the brain has done -On the horizon vs zenith position

Size-distance invariance explanation of the moon illusion

-Application of size-distance constancy. Horizontal moons provides distance cues that suggest moon is far away and therefore the brain perceives it is bigger (constructivist)

How could you test feedforward-feedback hypothesis

-Camprodon et al (2018) presented TMS over primary visual cortex at various times (20 ms to 300 ms) after stimulus onset -Participants had to identify if object was a mammal or bird -They found TMS disrupted performance most at 100ms and 220ms after stimulus presentation -Before the stimulus arrives to the brain, the brain has already shot feedback to the retina and other areas about what to expect to see (prepares them) -What would happen to moon illusion if we present TMS to visual cortex at different times after the presentation (viewing) of the moon?

Why does the moon appear larger when viewed on the horizon?

-Cog psych says start by deconstructing the differences: ---the reference frame (in the sky it's in a blank sky, on the horizon there are trees and buildings and other things in the way) ---You move your head up to see the moon when it's high but don't move it when it's low

Distance (depth) perception- Distance cues

-Color -Brightness -Motion parallax ---Objects that are closer are moving faster -Accommodation ---The way your lens adjusts -Linear perspective -occlusion/interposition ---If something is in front of another thing, it must be closer -shadow/shading -Texture ---As the texture changes to be closer together, it looks farther-- farther texture = closer to you -Aerial perspective -Relative height -Many of these cues are only present when viewing moon on the horizon

Size constancy

-Emmert's Law (1881)= size of retinal image projected by object changes in size as a linear function of distance object is away from eyes

Form agnosia and integrative agnosia

-Form agnosia= dorsal damage -integrative agnosia= ventral damage -Riddoch et al (2008) Two case studies SA (form agnosia) and HJA (integrative agnosia) -Object Recognition Test (form agnosia 60%, integrative 19%) -Effron shape test ((shapes on top of each other and ask patient to match to the shapes by themselves) form agnosia 74%, integrative 100%)

Real object advantage

-However, other research with visual agnosia patients has found that they can perform better object recognition for real-world solid objects (compared to 2D drawing and photographs of same objects) - 'real object advantage' -But unfortunately no one has tested moon recognition and moon size judgments by agnosia patients

Apparent-distance explanation for the size-distance paradox

-Kaufman & Rock (1960's) -2 step process for perceiving the moon 1) Unconscious registration of distance information (e.g., terrain means further away) -- bottom-up 2) Distance 'judged' on cognitive knowledge (e.g., larger objects are closer) - top-down -Illusion results from combination of bottom-up and top-down processing of distance (depth)

What role could knowledge play in moon illusion?

-Müller Lyer Illusion (the lines are the same size but the arrows look shorter than the opposite ---See 2D lines as part of a 3D world that we know -Would explain the weaker illusion experienced by people living in dense jungle environments (Segall et al., 1963) -Top-down explanations of illusions ---These illusions work because of our knowledge of the world and our familiarity with the size of objects

Moon Recognition

-Perceptual features of full moon -perceptual knowledge of moon -Idea that these are two different processes, if you can't do either it's double dissociation, not many documented cases of it, suggests 2 diff areas of the brain for processing these

Another example of distance perception affecting 'earlier' processing of visual information

-Sperandio et al (2012) -examined retinotopic activity in V1 while manipulating the size of after-images by moving the background various distances away from participant's head -Adjusting in the same kind of way as your car adjusts the brightness based on light conditions outside -Participants used their fingers to indicate the size of the afterimage -Perceived size of afterimage matched distance of background -Sperandio et al (2012) found that retinotopic activity in V1 changed as function of the distance of background (i.e., perceived size rather than actual size of image). No such change in V2 or V3.

Regions of the brain associated with visual agnosia

-Striate region of occipital cortex (red) V1 and extrastriate region of occipital cortex (yellow) V3, V4, V5/MT

Visual agnosia and illusions

-Turnbull et al (2004) -associative (integrative) agnosia patient DM (also amnesic) -Shape Detection test 19/20 -Unusual Views test 1/10 -DM copying drawing on right - fairly good but still some parts missing -OK on 2-D tasks but not good on 3-D versions of these tasks -rotation matching task involving 2-D rotations -OK performance -rotation matching task involving rotations in depth -v. poor performance -DM had great difficulty judging impossible figures (A & B) and did not show effect of visual illusions (C, D, & E) Would DM experience the moon illusion? ---Probably not, bc he doesn't know what it is, how far it is, etc.

Visual agnosia

-Two general categories of visual agnosia (Lissauer, 1890) -Form (apperceptive agnosia) ---can't really see shape -integrative (associative) agnosia ---can see the shape but still can't recognize the object -Visual agnosias generally result from damage to the extrastriate region of occipital cortex

Why do we see details of moon surface on horizon?

-What explains the subjective experience of seeing details of craters etc. only when the moon is seen on the horizon? -Lages et al (2017) tested whether visual acuity can be improved with illusion that is perceived to be larger (i.e. easier to see). They used the spiral motion aftereffect to make stationary images larger or smaller ---They found better letter recognition when tested after adapting to contracting motion (i.e., expanded after-image) -Could moon surface be seen on the horizon because of larger illusory-perceived size of moon that produces better visual acuity?

Size-distance paradox

-When the moon is bigger, you can see craters and other details on it -When it's in zenith you can't see the details as much -How can the horizon moon appear larger because it is further away (size-distance invariance) and yet at the same time it also appears nearer? -How can the brain think it's both farther (and makes it look bigger) and closer (and lets us see detail)

Atmospheric refraction

-explanation of the moon illusion -Explanation provided by Aristotle - similar to when looking at an object under water that appears bigger than really is. Refraction indices do not support degree of perceptual enlargement. However it may explain shape distortion seen for setting sun and moon. ---Flattening of upper edge due to refraction ---Small segment of curve gives appearance of having larger radius of curvature

How can distance be processed in two opposing ways at same time?

-fMRI study conducted by Murray, Boyaci, & Kersten (2006) -Rear sphere appears around 17% larger, even though the spheres are actually equal in size (the illusion) -Researchers measured size of activity in primary area of visual cortex V1 elicited by stimuli. -Found activity in V1 matched perceived size not actual size ---Results could reflect recurrent (feedforward & feedback) processing of distance perception not actual size perception -fMRI study conducted by Murray, Boyaci, & Kersten (2006) suggests illusion occurs before or at V1 stage of processing

Perceptual features of full moon

1) Shape= circular 2) color=white 3) Texture = random

Perceptual knowledge of moon

1) celestial object 2) sphere 3) very large inanimate object 4) Located a long distance away 5) located in sky (usually at night) 6) Solid mass 7) Cratered 8) Lit by sun 9) View-invariant object