Unit 7: Sensation and Perception
How raw energy hitting the eyes and ears becomes a seen and heard world, and what happens when the visual system is damaged or fooled.
7 topics · 23 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
Transduction and Absolute Threshold
- How it worksHow does a sensory receptor transduce physical energy, like light or sound, into a neural signal?
- Worked exampleFind why an absolute threshold is defined as the intensity detected 50 percent of the time, not 100 percent.
- Going furtherWhat happens to a person's absolute threshold for a stimulus after they've been sitting in the dark for twenty minutes?
Your turn1 of 2
A photon of light striking the retina eventually becomes a pattern of neural firing the brain can interpret, even though light itself is not an electrical signal. A student assumes there must be some direct, unmediated path from a physical stimulus to a mental experience of it. How does a sensory receptor actually transduce physical energy like light or sound into a neural signal?How the Eye Turns Light into Signals
- How it worksHow do rods and cones convert incoming light into electrical signals the optic nerve can carry?
- Common mistakeWhy isn't the eye simply a camera that records a picture and sends it to the brain?
- Going furtherWhat happens to color vision in dim light, when only the rods, and not the color-sensing cones, are active enough to respond?
Your turn1 of 2
Light enters the eye and, moments later, a pattern of electrical signals travels down the optic nerve toward the brain. A student pictures rods and cones as simply passing light straight through to the nerve, the way a window passes light through glass. How do rods and cones actually convert incoming light into electrical signals?The Visual Pathway and a Lesion Along It
- How it worksHow does visual information travel from the retina through the optic chiasm to the visual cortex at the back of the brain?
- How it worksHow does a lesion placed at a specific point along the visual pathway predict exactly which part of the visual field goes dark?
- Going furtherWhat happens to a person's field of vision when a lesion sits after the optic chiasm instead of before it?
Your turn1 of 2
Damage to the very back of the brain, far from the eyes themselves, can erase part of a person's vision entirely. A student assumes visual information must go directly from the eye to wherever it is consciously experienced, with no meaningful path in between worth tracing. How does visual information actually travel from the retina to the visual cortex?Depth Perception and Binocular Cues
- How it worksHow does binocular disparity, the tiny difference between what each eye sees, get turned into a sense of depth?
- Worked exampleFind why objects farther than about 20 feet away provide almost no usable binocular disparity for depth perception.
- Common mistakeWhy isn't depth perception impossible with only one eye, given that monocular cues like size and overlap still work?
Your turn1 of 2
Two eyes sit about 6.54 centimeters apart. An object sits 16.4 meters away. Using the small-angle approximation, binocular disparity in degrees is roughly the eye separation in meters divided by the distance in meters, converted from radians to degrees by multiplying by 180 over π. Find the disparity angle.Object Recognition and Gestalt Grouping
- How it worksHow do Gestalt principles like proximity, similarity, and closure group raw visual elements into objects?
- Going furtherWhat happens to Gestalt grouping when the elements in a scene are all moving together versus all sitting still?
- Common mistakeWhy isn't object recognition just a matter of matching a shape to a stored template pixel by pixel?
Your turn1 of 2
A flock of hundreds of individual birds in flight is seen as one flowing, moving shape rather than as hundreds of separate dots. A student assumes the visual system must be counting and tracking each individual bird separately to produce this unified impression. How do Gestalt principles like proximity, similarity, and closure actually group raw visual elements into one object like this?Color Vision and the Opponent Process
- How it worksHow does opponent-process theory pair red against green and blue against yellow further along the visual pathway?
- Common mistakeWhy isn't color vision fully explained by the three types of cones alone, without a second stage of processing?
- Going furtherWhat happens to color perception in a person who is missing one of the three cone types?
Your turn1 of 2
After staring at a bright red image for a while and then looking at a plain white wall, a person sees a vivid green afterimage where the red image had been. A student assumes this afterimage effect should not exist if color perception is fully explained by the three types of cones alone. How does opponent-process theory explain pairing red against green further along the visual pathway?Signal Detection and the Criterion
- How it worksHow do signal detection theory's overlapping noise and signal-plus-noise distributions produce hits, misses, false alarms, and correct rejections?
- Worked exampleFind how sliding the decision criterion to the right lowers false alarms but raises missed detections.
- Common mistakeWhy isn't a miss the same kind of error as a false alarm, even though both are wrong?
- Going furtherWhat happens to a person's criterion when the cost of missing a real signal goes up sharply?
- Ties togetherHow does the decision criterion in signal detection theory connect to the threshold used for statistical significance in hypothesis testing?
Your turn1 of 2
Out of 224 trials where a true signal is actually present, a radiologist correctly detects it as a hit on 36 of them. Find the number of misses.