Ch 1

Studying Sensation & Perception

Signal Detection Theory

  • Definition: The detection of stimuli involves both decision and sensory processes.

  • This theory helps to understand how decisions are made under conditions of uncertainty (e.g., hearing, smelling).

  • Our perception can vary based on external stimuli and personal responses.

Outcomes in Signal Detection

  1. Hit: Detecting a signal when it is present (correct detection).

  2. Miss: Failing to detect a signal that is present.

  3. False Alarm: Detecting a signal when it is absent.

  4. Correct Rejection: Not detecting a signal when it is absent (correctly identifying absence).

Signals and Noise

  • Signals: Useful, relevant information that one is actively looking for (e.g., correct answers on exams).

  • Noise: Irrelevant or false information that can interfere with detection, which can include:

    • Distractions in the environment (anxiety, external noise).

    • Other irrelevant stimuli that affect perception during tasks.

Criterion for Signal Detection

  • The internal threshold an individual sets to decide whether a signal is present, particularly in ambiguous situations.

Bias in Response

  • Liberal Bias: More likely to say "yes, signal present"; increases hits and false alarms.

  • Conservative Bias: More likely to say "no, signal absent"; increases correct rejections and misses.

Visual Search Tasks

  1. Feature Search: Target defined by a single feature (fast and efficient).

  2. Conjunctive Search: Target defined by a combination of features (more difficult and time-consuming).

Ganzfeld Experiments

  • Intended to study ESP; provides insight into sensory adaptations.

  • Sensory Receptors: Adapt to constant stimuli, leading to a fading perception over time (e.g., a constant visual field turning gray).

  • Some participants may experience hallucinations during the experiments.

Learning Objectives for Signal Detection Theory

  1. Explain outcomes of signal detection (hit, miss, false alarm, correct rejection).

  2. Define criterion and its impact on decisions (liberal vs. conservative bias).

  3. Describe visual search tasks: feature search vs. conjunctive search.

  4. Discuss what Ganzfeld experiments reveal about sensory adaptation.

Vision and Photoreceptors

Types of Photoreceptors

  • Rods: Sensitive to light intensity; used in night vision; do not detect color; located in the peripheral retina.

  • Cones: Sensitive to color; function best in bright light; concentrated in the fovea; respond to red, green, and blue light.

Visual Processing Pathway

  1. Retina: Converts light into neural signals.

  2. Optic Nerve: Carries visual information to the brain.

  3. Optic Chiasm: Where optic nerves partially cross paths, directing signals to respective hemispheres.

  4. Thalamus (LGN): Relay station for visual signals before they reach the visual cortex.

  5. Visual Cortex: Interprets visual inputs (color, shape, motion, depth).

What vs. Where Pathways

  • What Pathway (Ventral Stream): Carries information for object recognition; damage can lead to visual agnosia.

  • Where Pathway (Dorsal Stream): Processes spatial awareness; damage results in optic ataxia.

Effects of Damage to Visual Pathways

  • Optic Ataxia: Difficulty using visuospatial info to guide movement.

  • Hemispatial Neglect: Unawareness of one side of visual space.

  • Akinetopsia: Inability to perceive motion.

  • Apraxia: Difficulty producing voluntary movements.

Theories of Color Vision

Light and Color

  • Visual Light Spectrum: Human eyes can detect wavelengths from 380-700 nm.

  • Color Mixing:

    • Subtractive Mixing: Combining pigments (paints, inks).

    • Additive Mixing: Combining light sources (screen colors).

Theories of Color Vision

  1. Trichromatic Theory: Color perception from three cone types (red, green, blue).

  2. Opponent Process Theory: Neural responses to colors in opposing pairs (e.g., red-green, blue-yellow).

  3. Color Blindness Types:

    • Anomalous Trichromat: Reduced sensitivity to one primary color.

    • Dichromat and Monochromat: Complete absence of sensitivity to one or all primary colors.

Learning Objectives: Color Vision

  1. Define the impact of light properties (wavelength, intensity, saturation).

  2. Explain the contribution of trichromatic and opponent process theories to color vision.

  3. Discuss types of color blindness and visual perception alterations.

Perceiving the World

Visual Perception Insights

  • Perceptual Set: Expectations affecting interpretation of stimuli.

  • Inattentional Blindness: Failure to notice visible objects when attention is focused elsewhere.

Processing Types

  • Bottom-Up Processing: Building perception from sensory input.

  • Top-Down Processing: Utilizing pre-existing knowledge and expectations.

Visual Processing Models

  • Feature Detectors: Neurons respond to specific visual stimuli (orientation, movement).

Face Detection and Recognition

  • Specialized cells in the visual cortex focus on recognizing faces (social interaction).

  • Prosopagnosia: Inability to recognize faces due to impairment in neural pathways related to facial recognition.

Auditory Localization

Cues for Sound Localization

  1. Lateral Localization: Uses interaural timing and level differences to find horizontal sound positions.

  2. Median Localization: Uses monaural cues for vertical plane sound localization.

Learning Objective: Sounds Localization

  • Describe localization methods (lateral and median cues).