PSYC 104 Chapter 4- Sensation & Perception

Sensation: The process of detecting physical energy (stimuli) from the environment and converting it into neural signals.
Perception: The process of organizing, interpreting, and making sense of those sensations.
Transduction: Conversion of one form of energy into another (e.g., light into neural signals).

Bottom-up Processing: Sensory analysis that begins with the input (stimulus) and moves up to the brain’s integration of the information. Example: Breaking down a letter into parts before recognizing it.
Top-down Processing: Using experiences and expectations to interpret sensory information. Example: Reading jumbled words by focusing on context rather than individual letters.

Psychophysics: The study of the relationship between physical characteristics of stimuli and our psychological experience of them.
- Example: The relationship between light intensity and perceived brightness.

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

The minimum difference between two stimuli required for detection 50% of the time. It’s the smallest detectable change.

Definition: Diminished sensitivity to a stimulus as a result of constant exposure.
- Example: You stop noticing a band-aid on your arm after a while.

Definition: A mental predisposition to perceive one thing over another, influenced by experience and expectations (top-down processing).
Contextual Effects: The context or setting can influence perception. Example: In a certain context, we may perceive one object as larger than it is based on surrounding cues.

Our perceptions can be influenced by our current emotional state or motivation. Example: Depending on mood, some people see an old woman, while others see a young woman in ambiguous figures.

Transduction in Vision: The eye converts light energy into neural messages that the brain processes.
Light: A form of electromagnetic energy that stimulates the sense of vision.

Wavelength: Determines the color (hue) we perceive.
- Short wavelengths: Blues and purples.
- Long wavelengths: Reds and oranges.
Intensity: The amount of energy in a light wave (related to brightness). Higher amplitude means brighter light, lower amplitude means dimmer light.

Cornea: The transparent tissue that allows light to enter the eye.
Iris: A muscle that regulates the size of the pupil to control how much light enters.
Lens: Focuses light onto the retina.
Retina: The light-sensitive inner surface of the eye, containing:
- Rods: Detect black, white, and gray; crucial for peripheral and night vision.
- Cones: Detect color and are concentrated in the fovea (central vision).
Optic Nerve: Carries visual information from the retina to the brain.
Blind Spot: The point where the optic nerve exits the eye, and no receptor cells are present.
Fovea: The central focal point in the retina, where cones are concentrated.

Visual information travels from the retina to the optic nerve, then to the thalamus, and finally to the visual cortex in the brain for processing.

Trichromatic Theory: Young and von Helmholtz suggested that the retina contains three types of color receptors sensitive to red, green, and blue. When combined, these colors can produce the perception of any color.
Opponent-Process Theory: Suggests that we have opposing retinal processes (e.g., red-green, blue-yellow, white-black) that allow for color vision. Afterimage effects support this theory.

Figure-Ground: The organization of the visual field into objects (figures) that stand out from their background (ground).
Grouping Principles:
1. Proximity: Grouping nearby figures together.
2. Continuity: Perceiving smooth, continuous patterns.
3. Closure: Filling in gaps to create a complete, whole object.

Binocular Cues: Depth cues that depend on the use of two eyes.
- Retinal Disparity: The difference between the images received by each eye. The greater the disparity, the closer the object.
Monocular Cues: Depth cues available to each eye alone.
- Relative Height: We perceive objects higher in our visual field as farther away.
- Linear Perspective: Parallel lines appear to converge with distance (e.g., railroad tracks).

Lightness Constancy: The perception that the color and brightness of objects remain the same even under changing illumination.
Size-Distance Relationship: Objects of similar size appear different in size based on their distance from the viewer, as seen in illusions like the Ames room.

Kant vs. Locke:
- Kant: Perception is inborn and we are hardwired to organize sensory information.
- Locke: Perception is learned through experience.

Research (Blakemore & Cooper, 1970) has shown that sensory deprivation (e.g., kittens raised without exposure to horizontal lines) can impair the development of perceptual abilities.

Our visual system can adapt to artificially displaced or inverted visual fields. For example, people can adjust to wearing prism glasses that alter their visual input.