Sensation and Perception

Definition: Sensation is the detection of physical stimuli and the transmission of that information to the brain.
- Involves the basic experience of stimuli such as light, sound, food molecules, and changes in temperature and pressure.
- Key Point: Sensation encompasses only the detection part, without interpretation.

Definition: Perception refers to the brain’s processing, organization, and interpretation of sensory information.
- Involves conscious experience of the world and constructing useful and meaningful information from the sensations.
- Example: Sensation of sensing light (green traffic signal) processed into the perception of the command to "Go!"

Sensation and perception are integrated into experiences, with experiences guiding both processes.
Bottom-up Processing: Perception based on the physical features of the stimulus, building up perception by processing sensory aspects.
- Example: Recognizing root beer by processing its scent, moisture, and taste.
Top-down Processing: Interpretation shaped by knowledge, expectations, and past experiences. Context influences perception.
- Example: Not likely to perceive a blue apple as a real apple.

Context plays a vital role in how stimuli are recognized.
Examples:
- Incomplete letters leading to perceived words based on context.
- Difficulty in proofreading due to the brain’s tendency to fill in gaps and misinterpret stimuli through top-down processing.

Definition: The conversion of physical stimuli into electrical neural signals that the brain can process.
- Involves specialized sensory receptors that convert different types of stimulation (e.g., light, sound, chemicals) into neural impulses.
- Pathway: Most sensory information (except smell) first goes to the thalamus, which then relays it to specific areas of the cerebral cortex.

Visual System: Responds to light waves through rods and cones in the eye, with signals sent via the optic nerve.
Auditory System: Detects sound waves through pressure-sensitive hair cells in the cochlea, with signals sent via the auditory nerve.
Taste and Smell: Involve chemical stimulation and send information through specific cranial nerves to the brain.
Touch: Involves pressure on the skin, with signals sent through cranial and spinal nerves.

Qualitative Information: Basic characteristics of a stimulus (e.g., differences in musical notes or tastes).
Quantitative Information: Degree or magnitude of those qualities (e.g., loudness, brightness, or the relative saltiness of tastes).
- Quantitative differences are conveyed by the rate of neuron firing.

Definition: A decrease in sensitivity to a constant stimulus over time.
- Example: Noticing a smell initially but being unable to perceive it over time in a friend’s house.

Overview: Researchers recognize sensory thresholds are not absolute; they vary based on competing stimuli (internal and external noise).
Outcomes from Signal Detection:
- Hit: Detecting a presented stimulus.
- Miss: Failing to detect it.
- False Alarm: Reporting a detected stimulus when none was present.
- Correct Rejection: Accurately stating no stimulus was present.
Response Bias: Variability in how participants respond based on perceived stakes of detection.

Absolute Threshold: Minimum intensity required to detect a stimulus 50% of the time.
- Examples:
- Vision: A candle flame seen at 30 miles on a dark night.
- Hearing: The tick of a clock at 20 feet in quiet conditions.
- Taste: 1 teaspoon of sugar in 2 gallons of water.
- Smell: 1 drop of perfume diffused in six rooms.
- Touch: A fly’s wing falling on the skin.
Difference Threshold (Just Noticeable Difference): Minimum change between two stimuli that can be detected.
- Increases with stimulation intensity (Weber’s Law).

Overview: Studies the thresholds and relationships between physical stimuli and the psychological experiences they evoke.
Address means of detecting changes in stimuli (e.g., how much light must change before it is noticed).

Light Wavelengths: Determines color, visible light ranges from 400 to 700 nm.
- Color does not exist in objects but results from light wavelengths reflected towards our eyes.

Trichromatic Theory: Color arises from three types of cones sensitive to different wavelengths (S, M, L cones).
- Example: Yellow light stimulates L and M cones equally.
Opponent-Process Theory: Explains phenomena (e.g., color blindness and afterimages) where colors are perceived in opposites (red-green, blue-yellow).

Combines inputs from multiple senses; visualization results in a unified representation of sensory information.

Principles of Organization: Describe how we group sensory information to perceive cohesive objects.
- Proximity: Grouping things that are close together.
- Similarity: Grouping objects that are similar in appearance.
- Good Continuation: Preference for smooth, continuous shapes.
- Closure: Completing figures with gaps.

Definition: The perception of objects as stable despite variations in sensory data due to position, lighting, or background.
- Overcomes variability in size, color, lightness through relative judgments by the brain.

Human face recognition is unique, allowing for discernment of emotions and identity.
- Prosopagnosia: Condition where individuals cannot recognize faces but can identify objects.
- Inversion Effect: Faces perceived worse upside down, suggesting holistic processing.
- Thatcher Illusion: Demonstrates difficulty in noticing face feature rearrangements when inverted.

Human perception integrates sensory inputs into stable representations. Understanding sensation and perception helps uncover both the limitations and complexities of human awareness and interpretation.