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.