Sensation and Perception

Chapter 3: Sensation and Perception

Why Study this?

  • Exploration of dependence on senses:

    • Which sense do you rely on the most?

    • If you had to lose one sense, which would it be?

  • Topics of interest:

    • Orosensation & Dynamic Contrast

    • Connection to "Lord of the Rings" (LOTR)

    • Psychopaths and their olfactory capabilities

    • Reference: (Mahmut & Stevenson, 2012)

Defining Concepts & Approaches

  • Sensation:

    • Defined as the process by which energy receptors convert external stimuli into electrochemical signals.

  • Transduction:

    • Refers to the conversion of physical energy (e.g., light, sound) into neural signals.

  • Perception:

    • The process through which the brain interprets sensory information.

  • Psychophysics:

    • The study of the relationship between physical stimuli and psychological responses.

  • Gustav Fechner:

    • A key figure in psychophysics; explored absolute threshold defined as the minimum intensity of a stimulus required for detection 50% of the time.

  • Absolute Threshold:

    • Varies among individuals; highlights that we do not all share the same level of sensory sensitivity.

  • Difference Threshold (Just Noticeable Difference - JND):

    • The smallest difference in stimulation that can be detected 50% of the time; exemplified by Weber’s Law.

  • Signal Detection Theory:

    • Kelsey and the whistle scenario demonstrating how context affects the ability to discern stimuli in crowded situations.

Perception vs Awareness

  • Not all sensory information reaching the brain is consciously perceived:

    • Environmental noise may not be heard; awareness is selective.

  • Factors necessary for a successful Halo Party:

    • Doritos, Mountain Dew, Pizza.

  • Sensory Adaptation:

    • The decreased sensitivity to a stimulus after prolonged exposure, causing items such as rings, watches, or glasses to be noticed less frequently.

  • The brain is principally designed to detect novel stimuli while filtering out stable or constant features of the environment.

The Visual System

  • Wavelengths and Human Vision:

    • Electromagnetic Spectrum: Ranges from gamma rays (1 x 10^-14) to radio waves (1 x 10^4); visible light falls between approximately 400-700 nanometers (1 x 10^-7 to 7 x 10^-7).

  • Physical Dimensions of Light:

    • Wavelength: The distance between peaks affects our sense of color perception.

    • Amplitude: Determines the perceived brightness of color.

    • Purity/Saturation: The presence of white in color affects its purity.

Human Eye Anatomy

  • Key components:

    • Cornea: Transparent front layer that refracts light.

    • Pupil: Opening allowing light to enter.

    • Iris: Controls pupil size, regulating light entry.

    • Lens: Focuses light onto the retina.

    • Retina: Contains photoreceptor cells.

  • Additional structures:

    • Ciliary body: Controls lens shape.

    • Sclera: The white outer coat.

    • Choroid: Vascular layer providing nutrients.

    • Fovea centralis: Area of highest visual acuity.

    • Optic disc: Blind spot lacking photoreceptors.

    • Blood vessels: Supply the retina with nutrients.

    • Suspensory ligament: Supports the lens.

    • Optic nerve: Carries visual information to the brain.

Transduction of Light in the Retina

  • Process flow:

    • Incoming light stimulus → Rod and cone cells → Bipolar cells → Ganglion cells → Outgoing nerve impulse to cortex.

  • Photoreceptors:

    • Rods: About 120 million, responsive to low light.

    • Cones: About 6 million, essential for color vision and detail.

  • Example: Fourth of July fireworks illustrating rods and cones' response to changes in light.

Blind Spot and Perception

  • Defined:

    • The blind spot occurs where the optic nerve exits, and no photoreceptors are present, resulting in no light detection in this area.

  • In contrast, perception involves the interpretation and recognition of visual stimuli, raising questions about the nature of perceived reality (e.g., “If a tree falls in a forest…”).

Vision and Color

  • Sir Isaac Newton's Contribution:

    • His work established that color is not inherent in objects but is a perceptual process dependent on light wavelengths detected by our eyes.

  • Types of cones:

    • Red (long-wavelength)

    • Green (medium-wavelength)

    • Blue (short-wavelength)

  • Opponent Process Theory:

    • Proposes that color perception is influenced by opposing colors:

    • Green vs. Red.

    • Yellow vs. Blue.

Visual Processing Pathways

  • Optic Chiasm:

    • The crossing over of optic nerve fibers from both eyes, leading to processing in the brain.

  • Area V1:

    • Primary visual cortex located in the occipital lobe; responsible for simple visual processing:

    • Different lines activate different neurons.

    • Neurons specialize in shapes and edge orientation.

  • Blindsight Phenomenon:

    • Some patients with damage to the primary visual cortex may demonstrate the ability to respond to visual stimuli without conscious visual perception.

  • Dorsal and Ventral Pathways:

    • Dorsal pathway (where/how) processes spatial awareness; Ventral pathway (what) processes object recognition.

Gestalt Psychology

  • Fundamental Philosophy:

    • Gestalt psychology emphasizes that the whole is greater than the sum of its parts, leading to principles regarding how we perceive visual elements holistically rather than in isolation.

  • Key Gestalt Principles:

    • Closure: The perception of incomplete shapes as complete forms.

    • Continuity: Lines are perceived to continue in a manner that follows a smooth path.

    • Similarity: Elements that are similar are grouped together.

    • Proximity: Objects near each other are perceived as part of a group.

    • Linear Perspective: Perception of depth and distance through converging lines.

Other Depth Cues

  • Relative Size: Objects perceived as larger are seen as closer.

  • Relative Height: Objects higher in visual field are perceived as being farther away.

  • Interposition: Overlapping objects indicate which is in front.

  • Texture Gradient: Details become less distinct at a distance, suggesting depth.

  • Simplicity: Visual stimuli are perceived in the simplest forms possible.

Illusions of Perception

  • Ames Room:

    • Demonstrates that our perception of size can be distorted by the environment.

  • Illustrates the concept that vision can be deceptive; questions our understanding of perception realities.

  • Change-Blindness:

    • The phenomenon where changes in a visual scene go unnoticed, as shown in various demonstrations (e.g., video links).

  • Inattentional Blindness:

    • Failure to notice unexpected items in a visual display due to focus on specific stimuli.

Perceiving Motion

  • Motion perception is crucial to identify and track objects; involves changes in position on the retina.

  • Area MT:

    • A brain region specialized for processing motion information.

Perceiving Sound

  • Sound perception involves the interpretation of sound waves.

  • Core Attributes:

    • Pitch: Refers to the frequency of sound (high or low).

    • Loudness: The intensity or amplitude of sound.

    • Timbre: The quality or complexity of a sound.

  • Sounds are processed through the anatomy of the ear:

    • Outer Ear:

    • Pinna: The visible part of the ear.

    • Auditory Canal: Channel leading to the eardrum.

    • Eardrum: Vibrates in response to sound waves.

    • Middle Ear: Contains ossicles (hammer, anvil, stirrup), which amplify sound.

    • Inner Ear:

    • Cochlea: The structure in which auditory transduction occurs, shaped like a snail.

    • The Basilar Membrane: Vibrates in response to sound, stimulating hair cells that transduce sound signals.

  • Area A1:

    • Located in the temporal lobe, responsible for sound perception;

    • The left hemisphere processes language, while the right hemisphere processes music and rhythmic sounds.

Sound Frequency Processing

  • Place Code:

    • Primarily used for high frequencies; where the basilar membrane's reaction corresponds to specific frequencies.

  • Temporal Code:

    • Utilized for lower frequencies; the frequency of action potentials indicates frequency detected.

Localizing Sound

  • Sound localization relies on the relative position of the head and ears:

    • The closer ear receives a louder sound, indicating direction.

    • Factors affecting localization include how sound waves travel and the timing of sound arrivals at each ear.

Quick Thoughts on Pain

  • Pain is critical for survival, signifying potential harm.

  • Pain fibers are classified as:

    • Myelinated A-Delta Fibers: Transmit acute, sharp pain quickly.

    • Unmyelinated C-Fibers: Transmit slow, lingering pain.

  • Gate-Control Theory: Suggests mechanisms influence pain perception by integrating different types of stimuli.