Sensation and Perception

What is the role of our senses?

To take in the world by converting stimuli or sensory information into electrical signals processed by the brain.

What is the absolute threshold of a sensation?

The minimum stimulation needed to register a particular stimulus 50% of the time.

Examples of absolute threshold.

• Seeing a candle from 30 miles on a dark clear night

• Hearing the tick of a watch at 20 feet under quiet conditions

What is the signal detection theory model?

A model for predicting how and when a person will detect a weak stimulus, partly based on context. Detection of signals is affected by psychological state, alertness, and expectations.

What is the difference threshold?

The point at which one can tell the difference between two stimuli.

What is Weber's Law?

We perceive differences on a logarithmic rather than linear scale (It's the percent of change that matters).

What is transduction?

The process of transforming energy from light into neural messages.

What determines the hue (color or shade) that we see?

The light waves length and frequency.

What determines brightness or value?

The wave's amplitude.

What determines saturation or richness of color?

The number of distinct wavelengths that make up the light.

How do short waves with high frequency appear to our eyes?

As bluish colors.

How do long, low frequency wavelengths appear to our eyes?

As reddish hues.

What part of the eye focuses light waves onto the retina?

The lens.

What is the Chromostereoptic effect?

Pure colors located at the same distance from the eye appear to be at different distances (e.g., reds appear closer, blues more distant).

How is visual information encoded?

As separate neural impulses from tiny portions of the world, so the brain can reconstruct fine visual differences.

What are the two types of photoreceptor cells in the retina?

Rods and cones.

What is the function of rods?

Give us sensitivity under dim lighting conditions and allow us to see at night.

What is the function of cones?

Allow us to see fine details in bright light and give us the sensation of color.

Where are cones most tightly packed?

Around the fovea, the central region of the retina.

Where are rods primarily located?

In the periphery, the region surrounding the fovea.

What is the role of bipolar cells?

To turn on the neighboring ganglion cells.

What do the long axon tails of ganglion cells form?

The optic nerve, which carries neural impulses from the eye to the brain.

Where is the visual cortex located?

At the back of the brain in the occipital lobe.

What is the visual cortex responsible for?

The right cortex processes input from the left eye, and the left cortex processes input from the right eye.

What does the nervous system analyze as photo receptors capture light?

Differences in light (This Information gets transmitted to the brain).

How do we see objects?

By edge detection, where an edge can be created by a difference in color, brightness, or both.

What are feature detectors?

Specialized nerve cells in the visual cortex that respond to specific features like shape, angles, movements, and faces.

What is parallel processing?

The ability to process and analyze many separate aspects of a situation at once. (For visual processing this means making sense of form, depth, motion, and color.)

How does the brain use shadows?

To make decisions about what it's seeing and determine how objects are positioned in space.

What is Retinal disparity?

When viewing an object or scene, our left eye and right eye view slightly different images, providing information about distance.

What are monocular cues?

Depth perception cues that don't require both eyes. Examples include occlusion, relative size, relative height, texture gradient, familiar size, linear perspective, aerial perspective, and relative brightness.

What is occlusion?

The idea that an object that blocks the view of another object must be in front of it.

What is texture gradient?

As a texture gets further away, it forms smaller visual angles or pictures on the retina and is less noticeable.

What is linear perspective?

The idea that parallel lines seem to converge as they move into the distance.

What is aerial perspective?

Objects that are further away appear to be hazier and bluer.

What are Perceptional principles?

Organizational principles that explain how we tend to group things together.

What is the principle of similarity?

We group together figures that resemble each other.

What is the principle of proximity?

The closer figures are to each other, the more we tend to group them together perceptually.

What is the principle of good continuation?

A preference for organizing form in a way where contours continue smoothly along their original course.

What is the principle of closure?

We impose completeness on small amounts of input.

What is Pareidolia?

The tendency to organize incomplete and even random images into meaningful images.

What is nativism?

The view that perception of the world is a set of innate abilities.

What is empiricism?

The view that perception of the world is a set of acquired or learned skills.

What is top-down processing?

Perception is a constructive process that relies on past experience or stored information to interpret an unclear stimuli.

According to Richard Gregory, what is perception?

A hypothesis based on our prior knowledge.

What is bottom-up processing?

Perception involves build up from the smallest pieces of sensory information. It starts with the details and builds up to the big picture.

According to James Gibson, what is sensation?

Perception.

What are affordances?

Meanings that an environment has that guide behavior.

Are top-down or bottom-up processes always used?

No, perceptual research suggests that both top-down and bottom-up processes interact to produce the best interpretation of the world around us.

What s Familiar Size?

Knowledge of the normal size of certain objects can provides cues to depth.

What is Depth Perception?

Allows us to estimate distances between objects and ourselves.

How does information travel from eye to the brain?

The information slips through the optic nerve, the Thalamus, and finally the visual cortex.

What is the name of a color from a single wavelength?

Pure spectral color (called fully saturated)