Sensation and Perception

module 3

Absolute Threshold of Sensation

Minimum intensity of a stimuli needed to register another stimuli 50% of the time. It refers to the lowest level of stimulus that can be detected by an individual, such as sound, light, or taste.

Signal Detection Theory

A theory that predicts how and when a person will detect a weak stimulus, partly based on context.

Weber’s Law

We percieve differences on a logaritmic rather than linear scale. The percent of change matters.

Transduction

When the eye absorbs light that is then translated into neural messages that reaches the brain and forms what you actually see.

Wavelength and Frequency

Determines the hue that we see.

Wave Amplitude

Determines the brightness and intensity in what we see. The amount of energy in a given lightwave.

Greater amplitude

• Higher intensity

• Brighter color

Lower amplitude

• Lower intensity

• Duller color

Purity

Determines the saturation based on the number of distinct wavelengths that make up the light. Short waves with high frequency are registered in our eyes as bluish colors while long waves with low frequency, we register as reddish hues.

Light complexity determines saturation or purity

Pure spectral color

• Fully saturated

Greater number of spectral colors in a light, the lower the saturation

Chromostereopsis

Pure colors at same distance from the eye appears at different distances. Gives shapes plasticity and allows for depth perception by manipulating colors.

Retina

Contains photoreceptor cells called rods and cones

Rods

• Sensitivity under dim lighting conditions that allows us to see at night

• Rods is in the Periphery, surrounds the Fovea and is almost absent from the Fovea

Cones

• Fine details in bright light and gives us the sensation of color

• Tightly packed around the Fovea, central region of the retina and more sparsely elsewhere

Bipolar cells

• When stimulated, the rods and cones triggers chemical changes that sparks neural signals which in return, activates the cells behind them known as the bipolar cell

• Turns on the neighboring Gangilion cell

Gangilion Cells

• Braid together to form the ropey optic nerve that carries the neural impulses from the eye to the brain

This information travels from the optic nerve - thalamus - visual cortex

Visual Cortex

In the back of the brain in the Occipital lobe where the right cortex processes inputs from the left eye, and the left cortex processes inputs from the right.

Feature Detectors

In the visual cortex

• Shapes

• Angles

• Movements

• Faces

Parallel Processing

Ability to process and analyze many aspects of a situation at once

Visual Processing

making sense of

• Form

• Depth

• Motion

• Color

Links together individual features into whole objects

Retinal Disparity

When viewing an object or scene allows our left eye and right eye to view slightly different images.

Depth Perception

Allows us to estimate distances between objects and ourselves.

Monocular Cues

• Doesn’t require both eyes

• Occlusion

• Relative size, height, and brightness

• Texture gradient

• Familiar size

• Linear and Aerial perspective

Occlusion

An object that blocks the view of another object must be in front of it.

Texture Gradient

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

Forms smaller visual angles or pictures on the retina and is less noticeable.

Relative Height

Gives us the impression that objects that appear higher in our visual field are further away than objects that appear lower.

Familiar Size

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

Linear Perspective

Parallel lines seem to converge as they move into the distance

Aerial Perspective

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

Relative Brightness

Brighter images are closer and more shaded images are faded away.

Similarity

Grouping things together according to a principle of similarity.

Grouping figures together that resemble each other.

Form/Simplcity

Perceiving something in the simplest way.

Proximity

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

Good Continuation

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

Pareidolia

Tendency to perceive a specific, often meaningful image in a random or ambiguous visual pattern.

Closure

Filling in information to complete perceptions.

Nativism & Empricism

Bottom-up Processing vs. Top-down Processing

Top-down Processing

• Richard Gregory argued that perception is a constructive process that relies on top-down processing. Perception is a hypothesis based on prior knowledge. Involves a lot of constant, unconscious hypothesis testing

• James Gibson argued that perception involves innate mechanisms forged by evolution and that no learning is required. Perception is direct and not subject to hypothesis. Sensation is perception, What you see is what you get

  Affordances - meanings that an environment has that guides behaviors

Shape Constancy

Ability to perceive the shape of a rigid object as constant despite differences in the viewing angle