Sensory Processes - Chapter 4 Notes

  • Sensation: Raw experiences associated with stimuli (e.g., seeing a red object).

  • Perception: Integration and interpretation of sensory experiences (e.g., recognizing a fire engine).

  • Sensation involves sense organs and neural pathways; perception involves higher levels of the cortex.

  • Sensory Modalities: Systems that acquire and transduce environmental information into neural representations.

Characteristics of Sensory Modalities

  • Sensory systems convert environmental information into neural representations.

  • Understanding a sensory system involves understanding the relevant dimensions of environmental information and how they are translated.

  • Dimensions include intensity and other qualities.

Threshold Sensitivity

  • Absolute Threshold: Minimum stimulus magnitude that can be reliably discriminated from no stimulus (detected 50% of the time).

    • Psychophysical procedures measure the relation between physical stimulus magnitude and psychological response.

  • Difference Threshold (Just Noticeable Difference - jnd): Minimum difference in stimulus magnitude needed to tell two stimuli apart.

  • Weber-Fechner Law: The intensity increase needed to be noticed is proportional to the standard's intensity.

    • \Delta I = kI , where \Delta I is the increment threshold, I is the intensity of the standard, and k is the Weber fraction.

  • Psychophysical procedures have real-world applications (e.g., food manufacturing, lighting design).

Suprathreshold Sensation

  • Investigates the relationship between above-threshold stimulus intensities and sensory magnitudes.

  • Stevens' Law: Perceived psychological magnitude (Y) is a power function of physical magnitude (\Phi).

    • Y = k\Phi^r, where r is an exponent unique to each sensory modality.

  • Exponents less than 1.0 (e.g., loudness) produce concave-down curves; exponents greater than 1.0 (e.g., electric shock) produce concave-up curves.

Signal Detection Theory

  • Information consists of signal and noise; the task is to separate the signal from the noise.

  • False Alarm: Incorrectly reporting a signal when only noise is present.

  • Hit: Correctly reporting a signal when it is present.

  • Sensitivity: Ability to detect signals, measured by hit rate exceeding the false-alarm rate.

  • Allows separation of bias ($\beta) and sensitivity (d'$$).

Sensory Coding

  • Sensory systems translate physical information into neural representations.

  • Receptors: Specialized cells in sense organs that translate incoming physical information into an initial neural representation.

Visual System

  • Light: Electromagnetic energy with wavelengths between 400-700 nanometers.

  • Image Formation – cornea, pupil, and lens focus light on the retina.

    • Accommodation: the lens changes shape to focus on objects at different distances.

    • Myopia: nearsightedness; lens cannot flatten enough to focus on far objects.

    • Hyperopia: farsightedness; lens cannot become spherical enough to focus on near objects.

  • Transduction – rods and cones convert light into electrical impulses.

    • Rods: Low light, low resolution, colorless.

    • Cones: high light, high resolution, color.

    • Photopigments: light absorbing chemicals in rods and cones that trigger impulses.

    • Bipolar cells and ganglion cells transmit signals to the optic nerve.

    • Fovea: center of retina with high cone density.

    • Blind spot: where the optic nerve leaves the eye; no receptors are present.
      -Lateral inhibition: enhances edge detection by darkening one side of the edge and lightening the other.

Sensitivity

  • Rods activate at low light, cones at high light.

Seeing Patterns

  • Visual acuity is the ability to resolve details.

  • The edge, or contour, helps perceive the pattern.

Seeing Color

  • Short wavelengths (450-500 nm) appear blue, medium (500-570 nm) appear green, and long (650-780 nm) appear red.

  • Munsell system- specifies colored surfaces with hue name, and saturation/brightness numbers

Theories of Color Visions

  • Trichromatic Theory (Young-Helmholtz): Three types of cones sensitive to different wavelengths (short, medium, long).

  • Opponent-Color Theory (Hering): Visual system contains two types of color-sensitive units (red/green, blue/yellow).
    -Integrated two stage theory: combines theories using Trichromatic receptors and color-opponent units

Auditory System

  • Sound is generated by vibrating objects and is transmitted through air.

  • Pure tones are sine waves characterized by frequency and amplitude.

  • Frequency: Cycles per second (Hertz), corresponds to pitch.
    -High-frequency tones = high pitch.
    -Low-frequency tones = low pitch.

  • Amplitude: Pressure difference, corresponds to loudness (specified in decibels).

    • Soft whisper ~30 Decibels
      -Rock concert ~120 Decibels
      -Consistent exposure to >=100 decibels leads to hearing loss.

  • Timbre: Complexity of sound.

  • Outer ear gathers and focuses sound to the eardrum

  • Cochlea: contains 31,000 auditory neurons in auditory nerve sends signals to brain

Threshold Level

  • Intermediate frequencies > sensitivity to sound than high/low frequency levels.

Hearing Pitch

  • Young adults detect frequencies: 20-20,000 Hz.

Theories of Pitch Perception

  • Temporal vs. Place Theories

    • Temporal: overall basilar membrane vibrates (not accurate for every frequency

    • Place: frequency coded mechanically by resonance

Other Senses

  • Lack pattern and organization, but still important. Smell even has direct route to brain.

Olfaction

-Detects spoiled food or escaping gas; primitive and important sense.
-Insects secrete pheromones.
-Smell to signal other subtle matters like physiological functioning