Chapter 10 Perceiving Depth and Size Flashcards
Cue approach to depth
An approach that explains depth perception by identifying information in the retinal image (2-D), and also information provided by aiming and focusing the eye on an object that is correlated with depth in the scene.
Occulsion
Depth cue in which one object hides or partially hides another object from view, causing the hidden object to be perceived as being farther away.
According to cue theory how do we learn about the connection between cues and depth?
Through our previous experience with the environment. These associations are then made automatically by the brain.
3 major groups of cues
1) Oculomotor
2) Monocular
3) Binocular
Oculomotor cues
Depth cues based on our ability to sense the position of our eyes and the tension in our eye muscles. Indicates when an object is close.
How are oculomotor cues created? (what are the 2 oculomotor cues)
1) Convergence
2) Accomodation
Convergence
The inward movement of the eyes that occurs when we look at nearby objects
Accomodation
The change in the shape of the lens that occurs when we focus on objects at various distances.
Monocular cues
Cues that work with only one eye
3 major types of monocular cues
1) Accomodation
2) Pictorial cues
3) Movement based cues
Pictorial cues
Depth cues that can be depicted in pictures.
Relative height cue
Objects that have bases below the horizon appear to be farther away when they are higher in the field of view. Objects that have bases above the horizon appear to be farther away when they are lower in the field of view.
Relative size cue
When two objects are of equal size, the one that is farther away will take up less of the field of view
Perspective convergence
Perception that parallel lines in the distance convege (come together) as the distance of that line increases.
Familiar size cue
Using prior knowledge about the sizes of objects to make judgements about their distance
William Epstein (1965)
Showed that under certain conditions, our knowledge of an object’s size influences our perception of that object’s distance.
What stimuli did Eptsein use in his familiar size experiments?
Equal sized photogtaphs of different coins.
What happened in Epsteins experiment when observers used two eyes?
The coins no longer gave the perception of depth.
Atmospheric perspective cue
When distant objects appear less sharp and have a slgiht blue tint.
What creates the atmospheric persepective?
The farther away an object is, the more air and particles (dust, air pollution) we have to look through. Ex. Mountains that look 3 hours away in Philly will look 6 hours away in Montana due to different atmospheres.
Texture gradient cue
Elements that are equally spaced in a scene appear to be more closely packed as distance increases. In other words, objects equally spaced will appear closely packed at a farther distance.
Why are shadows useful?
- Shadows help determine the location of objects.
- Shadows enhance the 3-D of objects.
Motion-Produced cues
Depth cues created by movement
2 types of motion-prodced cues
1) Motion parallax
2) Deletion and accretion
Motion parallax cues
Occurs when, as we move, nearby objects appear to glide rapidly past us, but more distant objects appear to move more slowly. Ex. objects that speed by while looking out a moving car appear as blurs
What creates the perception motion parallax cues?
Images of near objects travel large distances across the retina. Images of far objects travel smaller distances across the retina.
Deletion (motion-produced) cue
Provides info about the relative depth of two surfaces. Occurs when a farther object is COVERED by a nearer object due to sideways movement of the observer relative to the objects.
Corresponding retinal points (Binocular disparity)
The points on each retina that would overlap if one retina were slid on top of the other. Receptors at corresponding points send their signals to the same location in the brain
Horopter (corresponding retinal points)
Imaginery surface that passes through the point of fixation and indicates the location of objects that fall on the corresponding points in the two retinas.
Noncorresponding points
Two points, one on each retina, that would not overlap if the retinas were slid onto each. Since the object is NOT located on the horopter the image falls on the noncorresponding points.
Angle of disparity (noncorresponding points)
The visual angle between the images of an object on the two retinas. When images of an object fall on corresponding points, the angle of disparity is zero. When images fall on noncorresponding points, the angle of disparity indicates the degree of noncorrespondence.
Random-dot sterogram
A pair of stereoscopic images made up of random dots. This stimulus contains no pictorial cues (ie. occulsion, relative height etc).
Ken-Ichino Tsutsui research on neurons that respond to pictorial depth
Using monkeys, he studied neurons in the parietal cortex that repsond to depth indicated by texture gradients. He showed that those neurons respond to both pictorial depth cues and binocular disparity.
Binocular depth cells/disparity-selective cells
Neurons in the striate cortex(VI) that respond to absolute disparity.
Gregory DeAngelis (1998) work with microstimulation
Used microstimulation on monkeys to activate a different group of disparity-selective neurons. Results showed that they shifted their depth judgement toward disparity signaled by the stimulated neurons.
A. H. Holway and Edwin Boring (1941) experiment on misperceving size in absence of depth information.
Observers change the size of the comparison circle in the left corridor to match his or her perception of the test circle on the right
Visual angle
Angle of an object relative to the observers eye.
Holway and Boring (1941) visual angle experiment
Found that eliminating depth information = difficulty in judging the physical sizes of the circles + size estimation is influenced by objects visual angle
Size constancy
Our perception of an objects size stays relatively constant even when viewed from different distances. Ex. solar elcipse.
Emmerts law
Size of an after image depends on the distance of the surface its viewed on. Farther away the surface, the larger the afterimage appears.
Muller-Lyer illusion (size illusion)
Two lines of equal length appear to have different lengths due to the “fins” at the end of the lines.
Ponzo (railroad) illusion
Two objects of equal size postioned between two converging lines appear different in size. According to misapplied scaling the top image appears larger due to depth info provided by the converging lines.
Ames room
Distorted room that makes two people of equal size appear different in size. The person with the smaller visual angle (smaller retinal image) is perceived as shorter.
Moon illusion
When the moon appears larger near the horizon then when it is high in the sky.
Apparent distance theory (moon illusion)
Idea that the horizon moon (viewed across a field of terrain) should appear farther than the higher moon(viewed in empty space) b/c the terrain contains depth info whereas empty space does not.
