PYSC Chapter 4-Perception

Chapter 4: Sensation and Perception

Introduction

• Sensation and perception are vital functions of the brain and sensory organs.

What are Sensation and Perception?

• Sensation: Detection of physical energy by our sense organs.

• Perception: The brain’s interpretation of these raw sensory inputs.

Transduction & Psychophysics

• The nervous system converts external stimulus into electrical signals within neurons.

• Psychophysics: Study of how we perceive sensory stimuli based on physical characteristics.

• Gustav Fechner (1860): Established foundational principles in psychophysics.

Absolute Threshold, JND & Weber's Law

• Absolute Threshold: The minimum level of stimulus intensity detected 50% of the time.

• Just Noticeable Difference (JND): The smallest change in intensity of a stimulus detectable.

• Weber’s Law: The JND is a constant proportion of the original stimulus intensity.

Signal Detection Theory

• Hit: Detected stimulus that was present.

• Miss: Failed to detect a stimulus that was present.

• False Alarm: Indicated a stimulus was present when it was not.

• Correct Rejection: Indicated no stimulus when none was present.

The Role of Attention

• Attention focuses on certain stimuli, possibly excluding others.

• Selective Attention: Focusing consciously on certain stimuli.

• Inattentional Blindness: Failing to perceive stimuli when focused elsewhere.

The Visual System

• Wavelength: Influences color perception. Different ranges impact how we experience light.

  • Visible light range: Approximately 400 nm to 700 nm.

The Eye

• Light enters through the pupil and is focused by the cornea and lens onto the retina.

• Accommodation: Lens changes shape to focus on objects at various distances.

The Retina

• The retina processes images, absorbs light, and sends information to the brain.

• Contains the fovea responsible for sharp visual acuity.

Rods and Cones

• Cones: Facilitate daytime and color vision.

• Rods: Assist in low-light (night) and peripheral vision.

Perceiving Shape and Contour

• Research by Hubel & Wiesel (1960s) revealed feature detection in response to specific patterns and orientations.

• Distinctions between simple and complex feature detector cells.

Perceiving Color

• Trichromatic Theory: Color perception based on three receptors (red, green, blue).

• Opponent-Process Theory: Color perception influenced by opposing responses (e.g., yellow vs. blue, red vs. green).

The Auditory System

• Sound waves are molecular vibrations traveling through a medium.

• Characteristics include amplitude, wavelength, and purity.

Structure of the Ear

• Outer, middle, and inner ear structures facilitate sound processing:

  • Parts include pinna, eardrum, cochlea, auditory nerve.

Perceiving Pitch

• Place Theory: Pitch perception tied to different locations on the basilar membrane.

• Frequency Theory: Pitch perception corresponds to the frequency of membrane vibration.

Taste and Smell

• Taste: Involves receptors for sweet, sour, salty, bitter, and umami.

• Smell (Olfaction): Detection through olfactory receptors including olfactory bulb.

Taste and Smell Perception

• Integration occurs in multiple brain regions:

  • Orbitofrontal cortex, olfactory bulb, somatosensory cortex, gustatory cortex.

Body Senses - Touch, Position, & Balance

• Body senses include touch, proprioception, and the vestibular system for balance.

  • Sensitive to pressure, temperature, and pain through various receptors.

Pain Perception

• Pain can result from various stimuli (heat, chemical, pressure).

• Signals transmitted via:

  • Fast Pathway (A-delta pathway)

  • Slow Pathway (C fibre pathway)

Proprioception

• Monitors body position to enable efficient movement.

• Proprioceptors sense stretch and force in muscles.

• The vestibular system assists with spatial orientation and gravity response.

Perception: Parallel Processing

• Ability to process multiple sensory modalities at once.

• Bottom-up processing: Constructing perception from sensory input.

• Top-down processing: Influence of beliefs and experiences on perception.

Perceptual Constancy

• The consistent perception of stimuli across varying conditions:

  • Size Constancy

  • Shape Constancy

  • Color Constancy

Gestalt Principles

• Perception governed by principles such as:

  • Proximity

  • Similarity

  • Closure

  • Continuity

  • Symmetry

  • Figure-ground relationships.

Face Perception

• Innate ability to recognize faces, evidenced by infants imitating facial gestures early.

Depth Cues

• Monocular Depth Cues: Visual information that can be perceived with one eye.

• Binocular Depth Cues: Require both eyes for perception, such as retinal disparity and converging focus.

Locating Sounds

• Auditory localization aided by ear placement and cues from sound intensity and timing.

Conclusion

• Understanding sensation and perception involves examining multiple systems and processes, allowing us to accurately perceive and interpret the world around us.