Depth--Slides Flashcards
Depth Perception
The brain uses many sources of information to determine distance and 3D shape.
Occulomter cues to depth. These are two hypothesis about how these circuts work: inflow hypothesis (A) and outflow hypothesis (B)
Occlusion cues. T intersections play an important role in depth perception from occlusion.
Perspective (texture gradient) cues
More perspective cue examples
Perspective and the vanishing point.
shading cues to depth and shape.
Flipping the previous slide over shows that the brain tends to interpet the shading cuses and the light as is coming from above
Almost all the shape seen in sand dunes (and faces)is due to shading/shadow. sand in the desrt (and skin on a face) is a fairly homogenous material.
Shading and perspective cues to depth and shape
Depth from shadows
Depth from shadows
Blur and visibility cues
The familiarity with the relative sizes of hands and heads can be used for distance judgment
Familiarity, perspective, occlusion and other clues.
Binovularity cues to depth and shape. When the eyes are fixed on the green square, objects at other distances fall on non-coressponding locations in the two eyes. The brain uses those disparities to judge relative depth.
Crayon distance
Random dot stereograms are useful for studying the disparity cue in isolation. They show that depth from disparity is not a mtter of recognizing objects i each eye and then comparing the positions of those objects. In fact, objects can be recognized from dispairty information alone.
Sharp edges are not required for seeing depth from binocular disparity
Pen Test, tests for depth perception
Disparity thresholds for different spatial frequency targes. For medium and high spatial frequencies disparity thresholds are small (down to 20 sec of arc or less)
Apparent depth as a function of disparity. THe black dots are disparities where there is no diplopia (double vision). The diagonal line shows that the locus of veridican (accurate) depth perception
Demonstration of binocular rivalry.
Measuring the responses of cortical neurons to binocular disparity. The vertical lines in B and C represent corresponding location in the two eyes.
Binocular receptive fields are receptive fields measure for both the left (L) and right (R) eye. Sometimes the shape is nearly the same in two eyes sometimes it is different. Neurons that have the same shape receptive field in both eyes will respond best to zero dispairty (if the receptive fields are in the same location). Binocular receptive fields can differ in shape, or position, or both between the two eyes.
Several types of binocular tuning functions are found in primary visual cortex. Each of these tuning functions is for an individual neuron.
Dr. Cormack’s lab has found that the typical range of disparities in the natural environment is moden (-1.5 deg to 1.5 deg_ and corresponds quite well to the range of disparity preferences that have been measured for disparity selective neurons in a cortical area known to process disparity and motion information.
Humans and Macaques can detect very small disparities, down to 20 sec or arc or less. The high stereo acurity provides very good depth information at close distance. The blue line shows the smallest detectable difference in distanse as a function of total distance from the eyes. The red line shows the difference in distance above which diplopia occurs.
motion cues to distance. When fixating the horizon while translating in a car or train, the nearer an object the faster it moves across the retina. When fixating a closer object while translating the farther an object from the fixated object, the faster it moves across the retina.
