Sensation and Perception Exam 1

Chapter 1: Introduction to Sensation and Perception

1.1 Sensation & Perception

• Sensation: Detecting a stimulus and possibly converting it into a private experience.

• Perception: Assigning meaning to a detected sensation.

• Key Senses: Visual, auditory, olfactory, gustatory, somatosensory + balance, thermoception, nociception, proprioception, interoception.

• Transduction: Conversion of a physical stimulus into a neural response via sensory receptors.

• Methods for Studying Sensation & Perception:

  • Thresholds: Identifying limits of perception.

  • Scaling: Measuring subjective experience.

  • Signal Detection Theory: Distinguishing signal from noise.

  • Sensory Neuroscience: Studying the biology behind sensory processes.

  • Neuroimaging: Brain activity visualization (e.g., fMRI, EEG).

1.2 Thresholds and Psychophysics

• Gustav Fechner: Founder of psychophysics (quantitative study of mind-body relationships).

• Key Terms:

  • Absolute Threshold: Minimum detectable stimulus.

  • Just Noticeable Difference (JND): Smallest detectable change in a stimulus.

  • Weber’s Law: JND is proportional to the stimulus level.

  • Fechner’s Law: Sensation magnitude increases logarithmically with stimulus intensity.

  • Signal Detection: Evaluates sensitivity and decision-making.

• Reaction Times:

  • Simple tasks: 200–250 ms (e.g., sound, touch, light).

  • Complex tasks (e.g., thermal detection): Up to 1 second.

1.3 Sensory Neuroscience

• Johannes Müller’s Doctrine: Sensation depends on the specific sensory fibers activated.

• Cranial Nerves:

  • Sensory: Olfactory (I), Optic (II), Auditory (VIII).

  • Motor: Oculomotor (III), Trochlear (IV), Abducens (VI).

• Neuronal Function:

  • Action Potential: Electrochemical process for neural communication.

  • Rate Coding: Firing frequency encodes information.

  • Temporal Coding: Spike timing encodes sensory variations.

• Neuroimaging:

  • EEG/ERP: High temporal resolution for electrical activity.

  • fMRI: Visualizes brain activity based on oxygenation changes.

1.4 Computational Modeling

• Models to Understand Perception:

  • Efficient Coding: Identifies sensory predictability.

  • Bayesian Models: Combines prior knowledge for predictions.

  • Artificial Neural Networks: Simulate biological neuron behavior.

• Deep Learning:

  • Uses large neural networks to classify information (e.g., object recognition).

  • Neuroscience & Vision Study Guide

    1. Light and Vision Basics

    • Light Properties:

      • A form of electromagnetic radiation; travels as waves or photons.

      • Interactions: Absorbed, Scattered, Reflected, Transmitted, Refracted.

    • Human Eye Components:

      • Cornea & Lens: Focus light on the retina via refraction.

      • Retina: Contains rods (low light) and cones (color, detail).

      • Optic Nerve: Transmits signals to the brain.

    • Accommodation: Lens shape adjusts for focusing.

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    2. Dark and Light Adaptation

    • Mechanisms:

      • Pupil dilation: Regulates light entry.

      • Photopigment regeneration: Adjusts to changing light conditions.

    • Duplex Retina:

      • Photopic (cones): High acuity, fast adaptation, active in bright light.

      • Scotopic (rods): High sensitivity, slow adaptation, active in dim light.

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    3. Retinal Processing

    • Photoreceptors:

      • Rods: Rhodopsin-sensitive, scotopic vision.

      • Cones: Trichromatic (red, green, blue-sensitive), photopic vision.

    • Horizontal Pathways:

      • Horizontal cells: Enable lateral inhibition (contrast enhancement).

      • Amacrine cells: Temporal sensitivity and contrast.

    • Vertical Pathways:

      • Bipolar Cells:

        • Diffuse: Input from multiple photoreceptors.

        • Midget: Input from single cones (fine detail).

      • Ganglion Cells:

        • P cells (Parvocellular): Fine acuity, color, shape.

        • M cells (Magnocellular): Motion detection, temporal changes.

    • Center-Surround Receptive Fields:

      • ON-center cells: Excited by central light.

      • OFF-center cells: Inhibited by central light.

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    4. Vision Disorders

    • Age-Related Macular Degeneration (AMD): Central vision loss due to macula degeneration.

    • Retinitis Pigmentosa (RP): Progressive peripheral vision loss caused by photoreceptor death.

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    5. Neural Signal Transmission

    • Phototransduction:

      • Light activates photoreceptors, causing hyperpolarization and decreased glutamate release.

      • Signals relayed to bipolar cells and then ganglion cells.

    • Fovea vs. Periphery:

      • Fovea: High acuity, cone-dominated.

      • Periphery: High sensitivity, rod-dominated.

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    6. Measuring Visual Information

    • Visual Angle: Determines how large an image appears on the retina.

    • Mach Bands: Perception of contrast at edges due to lateral inhibition.

  • Study Guide: Spatial Vision - From Spots to Stripes

    1. Visual Acuity

    • Definition: The smallest visual angle of a cycle of grating that can be perceived.

    • Types of Acuity:

      • Minimum visible acuity: Smallest object detectable.

      • Minimum resolvable acuity: Smallest separation between objects.

      • Minimum recognizable acuity: Smallest feature identifiable.

      • Minimum discriminable acuity: Smallest change in a feature that can be detected.

    • Measurement Methods:

      • Snellen Eye Chart: "20/20 vision" means normal vision at 20 feet.

      • Vernier acuity: Measures hyperacuity (e.g., alignment in a combination lock).

      • Contrast Sensitivity Function (CSF): Visibility of patterns depends on contrast and spatial frequency.

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    2. Retinal Ganglion Cells and Stripes

    • Spatial Frequency: Cycles of a grating per unit of visual angle.

    • Sine Wave Gratings: The visual system analyzes images using sine wave components (Fourier analysis).

    • Receptive Fields:

      • Center-surround organization: ON-center and OFF-center cells respond to contrast in the visual field.

      • Phase Sensitivity: Response depends on the position of a grating within a receptive field.

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    3. Lateral Geniculate Nucleus (LGN)

    • Structure:

      • Magnocellular layers (1-2): Large cells, motion detection, fast responses.

      • Parvocellular layers (3-6): Small cells, fine detail, and color.

      • Koniocellular layers: Role still under research.

    • Processing:

      • Ipsilateral: Same-side eye connection.

      • Contralateral: Opposite-side eye connection.

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    4. Striate Cortex (Primary Visual Cortex, V1)

    • Functions:

      • Transforms circular receptive fields from LGN into elongated stripe receptive fields.

      • Contains 200 million neurons.

    • Key Features:

      • Topographic Mapping: Spatial representation of the visual field.

      • Cortical Magnification: Fovea is overrepresented in V1 compared to the periphery.

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    5. Receptive Fields in Striate Cortex

    • Simple Cells: Respond to bars of light or dark.

    • Complex Cells: Respond to bars of light/dark and motion.

    • End-Stopping: Some cells prefer stimuli of a specific length.

    • Orientation Selectivity: Neurons respond best to specific orientations.

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    6. Columns and Hypercolumns

    • Columnar Organization:

      • Neurons in a column share the same orientation preference.

      • Hypercolumns: Contain all orientation preferences for a specific part of the visual field.

      • Ocular Dominance Columns: Preferential response to input from one eye.

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    7. Selective Adaptation

    • Definition: Prolonged exposure to a stimulus reduces neural response.

    • Examples:

      • Tilt Aftereffect: Adaptation to tilted lines distorts perception.

      • Spatial Frequency Adaptation: The brain adapts to patterns of specific frequencies.

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    8. The Development of Vision

    • Critical Period: Early childhood (4-5 years) is crucial for vision development.

    • Disorders:

      • Amblyopia: Reduced spatial vision in one eye.

      • Strabismus: Eye misalignment.

      • Anisometropia: Unequal refractive errors between eyes.

    • Early Intervention: Essential to prevent long-term deficits.

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    Key Takeaways

    ✔ Acuity: Ability to detect, resolve, and recognize objects.
    ✔ LGN: Processes visual input before sending it to V1.
    ✔ Striate Cortex (V1): Transforms and organizes visual information.
    ✔ Receptive Fields: Specialization for contrast, orientation, and motion.
    ✔ Development: Early visual experience shapes long-term function.

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