Sensation and Perception: Foundations, Thresholds, and Visual System

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Sensation and Perception

Introduction to Sensation and Perception

Sensation and perception are fundamental processes in psychology that allow us to experience and interpret the world around us. Sensation refers to the detection of physical stimuli from the environment, while perception involves the interpretation and conscious experience of those stimuli.

Sensation: The biological process of transducing physical stimuli from the external world into neural code. Sensory receptors differ depending on the sensory organ involved (e.g., photo receptors for vision).
Perception: The cognitive process of understanding and interpreting sensory information, allowing us to make sense of our environment.
Example: Sensory receptors in the eye detect light, which is then processed by the brain to perceive images.

From Stimulus to Perception

The pathway from stimulus to perception involves several steps, beginning with sensory receptors and ending with the interpretation in the cortex.

Sensory receptors → thalamus → cortex: Sensory information is relayed to the thalamus, which acts as a hub, sending signals to the relevant areas of the cortex for further processing.
Example: Visual information detected by the retina is sent to the thalamus and then to the visual cortex.

Stimulus Thresholds and Psychophysics

Psychophysics

Psychophysics is the study of the relationship between stimulus intensity and psychological experience. It explores how we detect and differentiate stimuli.

Absolute threshold: The minimum intensity required for a stimulus to be detected 50% of the time.
Difference threshold: The smallest difference in intensity required for a stimulus to be detected 50% of the time.
Weber's Law: States that the just noticeable difference between two stimuli changes proportionally to the intensity of those stimuli.
Example: Detecting the faintest sound in a quiet room versus a noisy environment.

Signal Detection Theory

Signal detection theory examines decision-making in the presence of uncertainty, considering both sensory experience and judgment.

All decision making takes place in the presence of some uncertainty.
Two types of correct responses: hit (detecting a present stimulus) and correct rejection (not detecting an absent stimulus).
Signal detection theory: Whether a stimulus is perceived depends on both the sensory experience and the judgment made by the subject.
Example: Determining if a faint sound is present or just imagined.

Subliminal Processing and Attention

Subliminal Processing/Perception

Subliminal perception refers to the detection of stimuli below the threshold of conscious awareness.

Priming: Prior exposure to a stimulus influences response to a related stimulus, shaped by context and expectations.
Divided attention: Paying attention to more than one stimulus or task at the same time.
Selective attention: Focusing on one particular event or task.
Example: Subliminal advertising may influence consumer behavior without conscious awareness.

Colour Vision and Light Properties

Properties of Light

Colour vision is based on the properties of light, including wavelength, amplitude, and purity.

Wavelength (hue): Determines the colour we perceive.
Amplitude (brightness): Determines the intensity or brightness of the colour.
Purity (saturation): Refers to the vividness or purity of the colour.
Example: Red light has a longer wavelength than blue light.

Vision: The First Sensory System

Structure and Function of the Eye

The human visual system is highly developed and allows us to perceive our environment in detail.

Sclera: The white, outer surface of the eye.
Cornea: The clear layer that covers the front portion of the eye and helps focus light.
Iris: The round muscle that adjusts the size of the pupil and gives eyes their colour.
Pupil: Expands to allow more light in and constricts to allow less light in.
Lens: Focuses light onto the back of the eye and changes shape for accommodation.
Transduction: Converts light into a neural message for the brain to interpret.

Retina and Photoreceptors

The retina is the inner lining of the eye, containing specialized receptors that absorb light and send signals to the brain.

Photoreceptors: Transform light into neural signals. Includes rods (sensitive to low light) and cones (responsible for colour vision).
Example: Rods help us see in dim light, while cones allow us to perceive colours.

Theories of Colour Vision

Trichromatic theory: Proposes three types of cones (short/blue, medium/green, long/red) responsible for different wavelengths.
Opponent-process theory: States that colour perception is based on opposing pairs (red-green, yellow-blue, white-black).
Example: Staring at a red image and then looking at a white surface may produce a green afterimage due to opponent-process cells.

Common Visual Disorders

Myopia (nearsightedness): Eyeball is elongated, causing distant objects to be out of focus.
Hyperopia (farsightedness): Image is focused behind the retina, making it difficult to see close objects.
Colour blindness: Most forms affect the ability to distinguish between red and green.
Example: People with myopia can see objects up close but not at a distance.

Term	Definition	Example/Application
Absolute Threshold	Minimum intensity required for detection 50% of the time	Detecting a faint sound in a quiet room
Difference Threshold	Smallest detectable difference in intensity	Noticing a change in brightness between two lights
Weber's Law	Just noticeable difference is proportional to stimulus intensity	Detecting weight difference between two objects
Signal Detection Theory	Detection depends on sensory experience and judgment	Deciding if a sound is present or imagined
Trichromatic Theory	Three types of cones for colour vision	Blue, green, and red cone activation
Opponent-Process Theory	Colour perception based on opposing pairs	Red-green, yellow-blue, white-black

Additional info: Academic context and definitions have been expanded for clarity and completeness. All key terms and processes have been explained with examples and applications relevant to college-level psychology.