S

PS262 module 1

The Perceptual Process

  • Stimulus in the Environment (Distal Stimulus)

    • Begins with an object in the external world (e.g., a tree)
    • Known as distal stimulus because it exists at a distance from the observer

  • Stimulus Hits the Receptors (Proximal Stimulus)

    • Light from the distal stimulus reaches the eye and creates proximal stimulus on the retina

  • Receptor Processes

    • Receptors in the eye (rods, cones) convert light energy into electrical signals through transduction
    • Unique properties of receptors influence perception

  • Neural Processing

    • Electrical signals generated by receptors transmitted through networks of neurons in the brain
    • Processes refine information and contribute to the perception of stimuli

  • Perception

    • Brain interprets neural signals to generate a perception of the object (e.g., recognizing the shape and color of a tree)

  • Recognition

    • The perceived object is compared with stored knowledge in the brain for identification
    • E.g., recognizing an object as a tree based on prior experience

  • Action

    • Individual takes action based on perception (e.g., walking towards the tree)
    • Perception and recognition can occur simultaneously or in reverse; actions can change our perception and recognition (e.g., identifying a tree more accurately after approaching it)

Distal and Proximal Stimuli (Steps 1 and 2)

  • Distal Stimulus

    • Refers to the stimulus out in the environment (e.g., the tree)

  • Proximal Stimulus

    • Refers to light reflecting from the distal stimulus which is captured by the sensory receptors

Key Principles

  • Principle of Transformation
    • Transformation occurs between distal stimulus and perception
  • Principle of Representation
    • Perception is based on representations formed on receptors and neural activity, rather than direct contact with stimuli

Receptor Processes (Step 3)

  • Transduction
    • Transformation of environmental energy (light, sound) into electrical energy
    • Example: Running fingers over tree bark produces electrical signals representing texture
    • Sensory receptors bridge the external sensory world and the internal representation of it

Neural Processing (Step 4)

  • Occurs after transduction
    • The tree is represented by electrical signals in sensory receptors

Measuring Perception

Absolute Threshold

  • The smallest stimulus level that can be detected (e.g., the smallest amount of salt needed to taste in soup)

Methods of Measuring Threshold

  • Method of Limits
    • Presenting stimuli in ascending/descending order to determine detection points
  • Method of Constant Stimuli
    • Presenting different stimulus intensities randomly; participant responds accordingly
  • Method of Adjustment
    • Participant adjusts the stimulus level until it is just barely detectable
  • Difference Threshold
    • Measures the difference between two stimuli (e.g., adding salt to detect differences in content)

Techniques for Perception Measurement

  1. Magnitude Estimation
    • Identifies perceptual magnitude of a stimulus
  2. Recognition Testing
    • Requires participants to categorize stimuli (testing recognition ability specific to brain function)
  3. Reaction Time
    • Time taken for a participant to respond after stimulus presentation
  4. Phenomenological Report
    • Describing properties of the stimulus (shape, size, color)
  5. Physical Tasks and Judgments
    • Examining interactions that follow perception (e.g., picking up an object)

Importance of Physical vs. Perceptual

  • Highlights the difference between actual stimuli and how we perceive them, e.g., lightbulb brightness perception versus actual measurements

Psychophysics: Key Terms

  • Action Potential
  • Absolute Threshold
  • Difference Threshold
  • Distal Stimulus
  • Neural Processing
  • Perception
  • Transduction
  • Perceptual Process
  • Psychophysics
    Modularity: Specific brain areas are specialized to respond to certain stimuli or functions

The Eye and Retina

Light and Vision

  • Vision relies on light reflection from objects
  • Electromagnetic Spectrum: Range of light energy, characterized by wavelength.

Eye Anatomy

  • Pupil: Opening for light entry
  • Cornea: Major focusing element (80% power)
  • Lens: Adjusts shape for focus on objects at varying distances (20% power)

Photoreceptors

  • Two types: Rods (for low light) and Cones (for color/bright light)
  • Phototransduction: converting light into electrical signals

Dark Adaptation

  • Process through which eyes adjust from bright to dark environments; involves cones and rods
  • Sensitivity Curves: Measuring different responses to light wavelengths

Visual Processing in the Retina

  • Neural Convergence: Multiple photoreceptors connect to single ganglion cells
    • Rods: High convergence (sensitive in low light)
    • Cones: Low convergence (better detail resolution)

Key Terms Related to Retina

  • Fovea: Area with only cones for detailed vision
  • Blind Spot: Area without receptors where optic nerve leaves the eye
  • Macular Degeneration: Condition affecting vision loss in central field due to fovea damage
  • Retinitis Pigmentosa: Condition causing peripheral vision loss affecting rods first

Spectral Sensitivity

  • Differences in wavelengths affect the sensitivity of rods and cones
  • Importance of pigment absorption for visual acuity and perception