Unit 4 Psych 101

Sensation

The stimulation of a sense organ; essentially the detection/observation of incoming sensory energy.

Perception

The selection, organization, and interpretation of sensory input; the process of translating sensory information into meaningful experience.

Sensation vs. perception

Sensation = detecting/stimulating sensory receptors with incoming information; perception = selecting, organizing, and interpreting that sensory information.

Five sensory systems covered

Sight/visual system, hearing/auditory system, taste/gustatory system, smell/olfactory system, and touch/tactile system.

General sensory pathway

Environmental stimulus → specialized sensory receptor → neural signal → initial processing in the brain.

Sensory adaptation

Reduced sensitivity to a stimulus after prolonged or repeated exposure.

Light

An electromagnetic radiation that travels in waves; humans can register only a small portion of the total range of wavelengths.

Visible light range

Humans can register approximately 400-700 nanometers of the electromagnetic spectrum.

Three physical properties of light waves

Amplitude, wavelength, and purity.

Light-wave amplitude

Brightness; greater amplitude is associated with greater perceived brightness.

Light wavelength

Color/hue.

Light purity

Saturation.

Amplitude → vision

Brightness.

Wavelength → vision

Color/hue.

Purity → vision

Saturation.

Eye pathway overview

Light enters the eye → cornea → pupil → lens → retina/receptors → neural information travels toward the brain.

Cornea

Window/front surface of the eye involved in receiving incoming light.

Lens

Focuses light rays onto the retina; accommodation changes its shape to focus.

Accommodation

Adjustment of the lens to focus images on the retina.

Pupil

Opening that regulates the amount of light passing to the rear of the eye.

Iris

Structure surrounding the pupil that helps regulate the amount of light entering the eye.

Retina

Neural tissue lining the inside/back surface of the eye; absorbs/registers light, processes images, and sends visual information toward the brain.

Visual receptors

Rods and cones located in the retina.

Rods

Visual receptors that play a key role in night vision and peripheral vision.

Cones

Visual receptors that play a key role in daylight vision and color vision and provide greater visual acuity than rods.

Rods vs. cones

Rods = night/peripheral vision; cones = daylight/color vision and greater acuity.

Fovea

Tiny spot in the center of the retina where visual acuity is greatest; contains only cones according to the class notes.

Optic disk

Area where the optic nerve exits the eye; corresponds to the blind spot.

Blind spot

Area associated with the optic disk where visual information cannot be directly registered because of the absence of visual receptors there.

Optic nerve

Carries visual neural information from the eye toward the brain.

Receptive fields

Collections of rods and cones that funnel signals to specific visual cells in the retina or brain.

Visual pathway

Main visual pathway projects through the thalamus, where signals are processed and distributed to the occipital lobe.

Thalamus in vision

Visual neural impulses are routed through the thalamus before being distributed to the primary visual cortex.

Primary visual cortex

Area in the occipital lobe responsible for initial cortical processing of visual input.

Occipital lobe

Brain lobe containing the primary visual cortex; major destination for visual information.

Secondary visual pathway

Handles coordination of visual input with other sensory input.

Feature detectors

Neurons that respond selectively to specific features of complex stimuli.

What happens after primary visual cortex processing?

Visual information is routed to other cortical areas along the where pathway/dorsal stream and what pathway/ventral stream.

Dorsal stream

"Where" visual pathway; associated with processing spatial/location-related aspects of visual information.

Ventral stream

"What" visual pathway; associated with identifying/recognizing what an object is.

Optic chiasm

Location associated with crossing of visual axons on their pathway toward the brain.

Lateral geniculate nucleus (LGN)

Thalamic structure involved in the visual pathway before information reaches the visual cortex.

Dark adaptation

Adjustment of the visual system to low-light/dark conditions.

Light adaptation

Adjustment of the visual system to brighter-light conditions.

Color perception

Color experience is related to wavelength and involves multiple theories of color processing.

Subtractive color mixing

Mixing that works by removing some wavelengths of light, leaving less light.

Additive color mixing

Mixing that works by putting more light into the mixture.

Trichromatic theory

The eye has three groups of receptors sensitive to wavelengths associated with red, green, and blue.

Opponent-process theory

Receptors make antagonistic responses to three pairs of colors; helps explain phenomena such as complementary colors and afterimages.

Trichromatic theory vs. opponent-process theory

Trichromatic theory emphasizes three receptor groups sensitive to red/green/blue wavelengths; opponent-process theory emphasizes antagonistic color pairs.

Afterimage

Visual experience that can remain after the original stimulus is removed; associated with opponent-process color theory.

Complementary colors

Opposing color relationships associated with opponent-process theory and afterimages.

Color blindness

Variation/deficiency in normal color perception; class notes connect it with color-processing mechanisms.

Color perception conclusion

Trichromatic and opponent-process theories are both necessary to explain color perception.

Form perception

Process of organizing visual input into meaningful forms or objects.

Same visual input, different perceptions

The same visual input can result in very different perceptions, demonstrating that perception is not simply a direct copy of sensory input.

Selective form perception

Form perception is selective, as illustrated by phenomena such as inattentional blindness.

Inattentional blindness

Failure to notice a visible stimulus when attention is directed elsewhere; demonstrates selective perception.

Feature analysis

Detecting specific elements/features of a stimulus and assembling them into complex forms.

Gestalt

From German, meaning "form" or "shape."

Gestalt theory

Approach emphasizing that perception organizes stimuli into meaningful wholes; "the whole is more than the sum of its parts."

Max Wertheimer

First put forth Gestalt theory in 1912 while describing the phi phenomenon.

Phi phenomenon

Illusion of movement created by presenting individual visual stimuli in rapid succession quickly enough that they are perceived as a whole; motion pictures are an example.

Core idea of Gestalt perception

The visual system organizes individual pieces of sensory input into meaningful, coherent wholes.

Gestalt principles

Figure-ground, proximity, closure, similarity, simplicity, and continuity.

Figure-ground

Organizing visual information by distinguishing a focal figure from its background; can produce reversible figures.

Reversible figure

A figure-ground image in which what is perceived as figure versus background can switch.

Proximity

Gestalt principle that elements close together tend to be perceived as belonging together.

Closure

Gestalt principle involving filling in missing information to perceive a complete object/form.

Similarity

Gestalt principle in which similar elements tend to be grouped together.

Simplicity

Gestalt principle favoring the simplest organization/interpretation of sensory information.

Continuity

Gestalt principle in which elements are organized into smooth or continuous patterns.

Gestalt principle mnemonic

Figure-ground, Proximity, Closure, Similarity, Simplicity, Continuity.

Bottom-up processing

Perceptual processing that begins with individual sensory features/details and builds toward perception of a whole.

Top-down processing

Perceptual processing influenced by expectations, knowledge, and perceptual hypotheses when interpreting stimuli.

Bottom-up vs. top-down

Bottom-up = individual sensory information → whole perception; top-down = hypotheses/expectations/knowledge influence interpretation of incoming stimuli.

Perceptual hypothesis

An inference about the form that could be responsible for the sensory stimuli being received.

Perceptual set

Readiness or tendency to perceive a stimulus in a particular way.

Feature analysis and bottom-up processing

Class notes associate feature analysis with detecting individual components and assembling them into a whole, making it a bottom-up process.

Perceptual hypotheses and top-down processing

Existing expectations/inferences influence how incoming stimuli are interpreted.

Perceptual constancies

Tendency to perceive important properties of objects as relatively stable despite changes in sensory input.

Depth perception

Perception of distance and three-dimensional space.

Two broad categories of depth cues

Binocular cues and monocular cues.

Binocular cues

Depth cues based on the differing views of the two eyes.

Monocular cues

Depth cues about distance that can be obtained from the image in either eye alone.

Retinal disparity

Binocular depth cue based on the fact that the right and left eyes see slightly different views of objects within roughly 25 feet.

Pictorial cues

Monocular depth cues that can be represented in a flat picture.

Examples of pictorial depth cues

Linear perspective, texture gradients, relative size, height in plane, interposition, and light and shadow.

Linear perspective

Pictorial depth cue in which parallel lines appear to converge with increasing distance.

Texture gradient

Pictorial depth cue involving changes in the detail/density of texture with distance.

Relative size

Pictorial depth cue in which apparent size differences help indicate relative distance.

Height in plane

Pictorial depth cue in which position within the visual field contributes to perceived distance.

Interposition

Pictorial depth cue in which one object blocking another suggests the blocking object is closer.

Light and shadow

Pictorial cues using illumination/shading to provide information about form and depth.

Visual illusion

A discrepancy between the appearance of a visual stimulus and its physical reality.

What do visual illusions demonstrate?

Perceptual hypotheses can be wrong, showing that perception is not simply a direct reflection of objective reality.

Examples of visual illusions

Müller-Lyer illusion, Ponzo illusion, and moon illusion.

Müller-Lyer illusion

Example of a visual illusion demonstrating a discrepancy between appearance and physical reality.

Ponzo illusion

Example of a visual illusion in which depth/contextual information alters perceived size.

Moon illusion

Example of a visual illusion involving differences in the perceived size of the moon depending on context/location.