Perception and Visual Processing
Characteristics of Light Energy
Visible Light: The energy our eyes perceive is light energy, a form of electromagnetic radiation.
Not just colors, but waves of electromagnetic energy.
Electromagnetic Spectrum: Ranges from gamma rays (short wavelengths) to radio waves (long wavelengths).
Wavelengths visible to humans: from blue-violet (short) to red (long).
Properties of Light Waves
Wavelength: Distance from one wave peak to another.
Determines hue (color) of light (e.g., red petals, green leaves).
Amplitude: Height of the wave.
Influences the intensity (brightness) of the light.
Frequency: Number of complete wavelengths that pass a point in a given time.
Shorter wavelengths = higher frequency; relates to perceived color.
The Eye as a Visual System
Light Entry: Light enters the eye through the cornea.
Cornea: Bends light for focus.
Pupil: Adjustable opening controlled by the iris to control light intake.
Iris: Colored muscle that dilates or constricts with light intensity and emotional state.
Lens: Focuses light rays into an image on the retina.
Accommodation: The process of the lens changing curvature for focusing.
Vision Disorders
Nearsightedness (Myopia): Occurs when the lens focuses images in front of the retina.
Can be corrected with glasses, contact lenses, or surgery.
Visual Processing Pathway
From Retina to Brain: Light triggers the retina's photoreceptor cells (rods and cones), activating bipolar cells, leading to ganglion cells, which form the optic nerve.
Blind Spot: Area without receptor cells where the optic nerve leaves the eye; brain fills in this gap.
Rods and Cones
Rods: Light-sensitive for dim light, black-and-white vision; numerous (120 million).
Located in the retina's outer regions; low detail sensitivity.
Cones: Sensitive to color (red, green, blue); fewer (6 million), located around the fovea; high detail sensitivity.
Connection to Brain: Cones have a 'hotline' to the brain, sending precise information; rods work together to provide cumulative signals.
Color Perception
Trichromatic Theory: Developed by Young-Helmholtz; suggests three types of color receptors sensitive to red, green, and blue.
Colors perceived through combinations stimulating these cones (e.g., red + green = yellow).
Color Deficiency: Condition affecting ability to distinguish colors, often red-green deficiency.
Opponent Process Theory: Suggests additional color processing in opposing pairs (e.g., red-green, blue-yellow).
Feature Detectors in the Brain
Feature Detectors: Neurons in the visual cortex responding to specific visual features such as edges, lines, angles, and movement.
Specialized cells analyze visual patterns and relay complex integrations of stimuli to higher processing areas.
Parallel Processing in Vision
Parallel Processing: Brain processes multiple aspects of visual information simultaneously (motion, form, depth, color).
The Face Recognition System: Specific neural networks for facial recognition, crucial for social interactions.
Depth Perception
Binocular Cues: Include convergence and retinal disparity; important for judging distances with two eyes.
Example: Touching pen tips together with both eyes open is easier than with one closed.
Monocular Cues**: Depth cues available through one eye; include linear perspective, interposition, relative size, etc.
Motion Perception: Brain interprets motion based on the direction and speed of objects to provide a cohesive sense of movement.
Perceptual Constancy**: Ability to perceive objects as stable despite changes in conditions affecting our perception (brightness, color, shape).
Shape and Size Constancy: Recognizing familiar objects as constant in form despite changes in perspective or distance.
Perceptual Adaptation**: Ability to adjust sensory perceptions based on context and experience; crucial for maneuvering through changing visual fields.
Research on Adaptation: Studies of visual perception involving goggles that invert visual fields show our capacity to adapt to radically distorted environments.