Sensation and Perception Exam 1

WashU

What is the absolute threshold?

The minimum stimulus intensity detected 50% of the time.

Why is the absolute threshold probabilistic?

Detection varies across trials; threshold is defined at 50% detection.

A stimulus is detected 50% of the time. What does this indicate?

Its intensity is approximately the absolute threshold.

What is the difference threshold (JND)?

The smallest detectable difference between two stimulus intensities.

What does Weber’s law predict?

JND is a constant proportion of the standard intensity.

If a 100-g standard has a 2-g JND, what is Weber’s fraction?

0.02, because JND ÷ standard = 2 ÷ 100.

If intensity increases, what happens to JND under Weber’s law?

JND increases proportionally with the standard.

Why can 1 oz vs. 2 oz feel different but 321 vs. 322 oz not?

JND depends on proportional, not absolute, change.

What does Fechner’s law assume?

Weber’s law is true and each JND feels equally large.

What does Fechner’s law predict about equal physical increments?

They produce progressively smaller perceived increments.

Why did Stevens argue Fechner’s law was insufficient?

Weber’s law is not always accurate across sensory modalities.

What does Stevens’ power law relate?

Physical stimulus magnitude to perceived magnitude.

In Stevens’ law, what does n > 1 mean?

Perception increases faster than physical intensity; response expansion.

In Stevens’ law, what does n < 1 mean?

Perception increases slower than physical intensity; response compression.

In Stevens’ law, what does n = 1 mean?

Perceived magnitude increases at a constant rate.

What is the method of limits?

Stimulus intensities are presented in an orderly ascending or descending series.

Why can method of limits produce habituation/preservation errors?

People may keep responding as if the stimulus is present.

Why can method of limits produce anticipation errors?

Participants may remember the pattern or expected transition point.

How can anticipation errors be reduced?

Stagger the starting point of successive series.

How does method of adjustment differ from method of limits?

The stimulus is continuously adjusted by the subject or experimenter.

Why is method of constant stimuli more accurate?

Fixed intensities are presented randomly rather than in an orderly sequence.

What is a key disadvantage of constant stimuli?

It requires many trials.

How does the staircase method determine threshold?

Intensity reverses direction after detection changes; threshold is average reversal intensity.

What is the standard in a difference-threshold experiment?

The reference stimulus against which a comparison is judged.

What is the comparison stimulus?

A stimulus whose intensity varies relative to the standard.

What problem does signal detection theory address?

Separating sensory sensitivity from response bias.

Why can two people with equal sensitivity respond differently?

They may have different decision criteria or response biases.

In signal detection theory, what is a hit?

Correctly detecting a signal when one is present.

What is a miss?

Failing to detect a signal that is present.

What is a false alarm?

Reporting a signal when none is present.

What is a correct rejection?

Correctly reporting no signal when none is present.

What is sensitivity in signal detection theory?

The true-positive rate, or hit rate.

What is specificity?

The true-negative rate, or correct rejection rate.

On an ROC graph, what indicates greater sensitivity?

A curve closer to the upper-left region.

What does the diagonal ROC line represent?

No sensitivity; performance is essentially chance.

How can payoffs change detection responses?

Changing the cost of errors can shift response criterion without changing sensitivity.

Why is signal detection useful for medical tests?

It distinguishes sensitivity from consequences of false alarms and misses.

What is transduction?

Converting physical stimulus energy into neural activity.

What is a sensory receptor's special role?

It transduces physical energy into electrical/neural signals.

What are the three major parts of a neuron?

Soma, dendritic tree, and axon.

Where does neuronal input primarily arrive?

At the cell body and dendritic tree.

Where does neuronal output travel?

Along the axon.

What is the resting potential?

About -70 mV inside the neuron relative to outside.

During depolarization, which ion flows into the neuron?

Sodium (Na+).

During repolarization, which ion flows out?

Potassium (K+).

What does all-or-none mean for action potentials?

Once threshold is reached, the action potential occurs fully rather than partially.

What is the refractory period?

A period after an action potential when another cannot immediately occur.

What is a synapse?

The gap between neurons across which neurotransmitters communicate.

What is light physically?

Electromagnetic radiation characterized by wavelength, intensity, and composition.

What psychological property corresponds to wavelength?

Hue.

What psychological property corresponds to light intensity?

Brightness.

What psychological property corresponds to spectral composition?

Color/spectral appearance, including saturation.

What is the cornea's role?

It is the transparent front membrane through which light enters the eye.

What controls the amount of light entering through the pupil?

The iris.

What is the pupil?

The opening in the center of the iris through which light enters.

What is the retina?

The neural membrane containing photoreceptors that convert light into signals.

What happens during phototransduction?

A photon changes photopigment shape, altering neurotransmitter release.

Why don't we normally notice the blind spot?

The perceptual system fills in missing information.

Where are cones most densely concentrated?

The fovea.

Where are rods absent?

The fovea.

Which photoreceptors are more light-sensitive?

Rods.

Which photoreceptors provide better spatial acuity?

Cones.

Why do rods have greater sensitivity?

Greater convergence allows signals from many rods to influence a ganglion cell.

Why do cones provide higher acuity?

They have less convergence, preserving spatial information.

What is the Purkinje shift?

With dark adaptation, vision shifts from cone-dominated toward rod-dominated sensitivity.

Why can red light preserve dark adaptation?

Rods are relatively insensitive to long wavelengths.

Why might a dim object be easier to see off-center?

Peripheral retina contains many rods, which are highly light-sensitive.

What is spatial summation?

Combining signals across receptors to increase sensitivity.

What is lateral inhibition?

Activated receptors reduce signaling from neighboring receptors.

What perceptual function does lateral inhibition enhance?

Edges and differences in stimulation.

What causes Mach bands?

Lateral inhibition enhances perceived brightness differences at boundaries.

Why does simultaneous contrast occur?

Surrounding stimulation alters the response to a central stimulus.

What is a receptive field?

The sensory area whose stimulation changes a neuron's activity.

How do retinal receptive fields differ from cortical receptive fields?

Cortical fields are generally more specialized for particular stimulus features.

What do simple cortical cells respond especially well to?

Bars of light at preferred orientations.

How do complex cells differ from simple cells?

They can respond to stimuli across locations and often code motion, color, or size.

What are feature detectors?

Neurons that respond preferentially to particular stimulus features.

Why does a feature detector's response alone not prove it causes perception?

Correlation between firing and perception does not establish causal involvement.

What does selective adaptation reveal about feature detectors?

Fatiguing neurons tuned to a feature produces a selective perceptual aftereffect.

What is retinotopic mapping?

Neighboring locations on the retina map to neighboring brain locations.

What is cortical magnification?

The fovea receives disproportionately large cortical representation.

What happens as visual processing moves from retina to cortex?

Receptive fields generally become increasingly specialized.

What is the dorsal visual pathway associated with?

Action and spatial information—often described as "where/how."

What is the ventral visual pathway associated with?

Perception and object recognition—often described as "what."

What does inferotemporal cortex contribute to?

Object recognition based on complex shapes and contours.

What does MT/MST contribute to?

Processing visual motion.

What is the fusiform face area (FFA) specialized for?

Processing faces.

What is the extrastriate body area (EBA) associated with?

Processing body parts.

What is the parahippocampal place area (PPA) associated with?

Processing places/scenes.

What is modularity in visual processing?

Some brain areas show preferences for particular stimulus categories.

Why does distributed coding complicate strict modularity?

Multiple overlapping areas can contribute to processing a stimulus.

What is the binding problem?

How separate representations of color, shape, motion, etc. become one unified percept.

What may help solve the binding problem?

Synchronized neural activity and attention.

What is population coding?

A stimulus is represented by activity across multiple neurons.

What is an additive color mixture?

Mixing lights so all wavelengths present in each component remain in the mixture.

What is a subtractive color mixture?

Mixing pigments or filters that remove wavelengths from the available light.

What are complementary colors?

Pairs that combine in equal proportions to appear gray.

What is spectral power distribution?

The wavelengths of light emitted by a light source.

What is spectral reflectance?

The wavelengths of light reflected by an object.

What is color contrast?

A target appears shifted toward the complementary color of its surround.