Vision Flashcards
What is visual acuity?
The ability to see fine detail
How can visual acuity be tested?
Snellen chart
What does it mean to have 20/20 vision?
The smallest line of text the average person can read from 20 feet away
How do we see?
Sensory receptors in eyes respond to wavelengths of visible light energy (part of electromagnetic spectrum we can see)
What psychological dimension does wavelength refer to?
Colour
What psychological dimension does amplitude refer to? Purity?
Brightness and saturation
What happens when light reaches the eye?
It passes through the cornea (outer tissue), which bends the light wave and sends it through the pupil
What is the iris?
Coloured part of the eye and a muscle that controls the size of the pupil
What do muscles behind the iris do?
Control the shape of the lens to bend the light wave and focus it onto the retina
What is the retina?
Light sensitive tissue lining the back of the eyeball
What is accommodation?
The process by which the eye maintains a clear image on the retina
What happens if someone is farsighted?
Light is focused behind retina
What happens if someone is nearsighted?
Light is focused in front of retina
What are photoreceptor cells?
Cells on the retina that contain light sensitive pigments that transduce light into neural impulses
What do cone cells do?
Detect colour, operate under normal daylight conditions and allow us to focus on find details
What do rod cells do?
Become active under low light conditions for night vision
What is the fovea?
An area of the retina where vision is the clearest and there are no rods at all
What are the three major cone types?
S: responds to short wavelengths (blue)
M: responds to medium wavelengths (green)
L: responds to long wavelengths (red)
What is trichromatic colour representation?
The pattern of responding across the three types of cones provides a unique code for each colour
What is colour deficiency?
Genetic disorder in which one cone type is missing
What is the colour opponent system?
Pairs of visual neurons work in opposition and a neuron corresponding to one colour fires less in response to wavelengths corresponding to the opposite colour
What’s the ventral stream?
Visual pathway that travels across the occipital lobe into the lower levels of the temporal lobes. Include brain areas that represent an object’s shape and identity.
What’s the dorsal stream?
Visual pathway that travels up from the occipital lobe to the parietal lobes. Connects with areas that identify the location and motion of an object.
What’s visual-form agnosia?
The inability to recognize objects by sight due to damage to the ventral stream. Can still guide movements by sight though.
What’s optic ataxia?
Difficulty using vision to guide their reaching and grasping movements, but can still recognize objects.
What’s inattentional blindness?
Failure to perceive objects that are not the focus of attention
What’s change blindness?
People fail to detect changes to the visual details of a scene
What are image based recognition theories?
Objects are stored in memory as a template (mental representation that can be directly compared to a viewed shape in the retinal image)
What’s the problem with image based recognition theories?
Recognition time is not dependent on object orientation
What are parts based recognition theories?
The brain deconstructs viewed objects into a collection of parts called geons. Objects are stored in memory as structural descriptions.
What is the problem with parts based recognition theories?
Object recognition only at the level of categories (i.e. how do you distinguish your mother’s face from a stranger’s)
What are monocular depth cues?
Aspects of a scene that yield information about depth when viewed with only one eye. Rely on the relationship between distance and size.
What are examples of monocular depth cues?
1) Relative/familiar size: smaller objects look farther
2) Linear perspective: parallel lines appear to meet as they travel into the distance
3) Texture gradient: texture becomes less and less apparent the farther it goes into the distance
4) Interposition: when one object overlaps another, the object that is partially obscured is perceived as being farther away
5) Relative height to the image
Ames room
The effect works by utilizing a distorted room to create the illusion of a dramatic disparity in size. While the room appears square-shaped from the viewers perspective, it is actually has a trapezoidal shape.
What is binocular disparity?
Binocular depth cue. The difference in the retinal images of the two eyes that provides information about depth. Brain uses this information to perceive how far away objects are.
