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