Sensation and Perception

SENSATION AND PERCEPTION

Introduction to Sensation and Perception

  • Sensation and perception are fundamental processes by which we become aware of the world around us.

Sensation vs. Perception

  • Sensation: The physical processing of environmental stimuli by the sensory organs.

  • Perception: The psychological process of interpreting sensory information.

Sensory Receptors and Neural Impulses

  • Sensory receptors detect environmental stimuli such as light, sound, and smell.

    • Example: Eyes, ears, and nose serve as sensory organs.

  • Conversion of stimuli into neural impulses known as transduction occurs in perception areas such as visual, auditory, and olfactory areas.

Factors that Influence Perception

  • Psychophysics: A field that systematically relates the physical characteristics of a stimulus to an observer’s perception.

    • Key concept: Measurement of thresholds that indicate the minimum intensity of a stimulus.

Absolute Threshold

  • Definition: The smallest amount of stimulation needed for detection by a sensory system 50% of the time.

  • Example: The olfactory bulb has approximately 300 million olfactory receptors contributing to the detection of smells.

Just Noticeable Difference (JND) or Difference Threshold

  • Definition: The minimum difference between two stimuli needed for detection 50% of the time.

  • Illustration: Identifying the weight difference between two dumbbells (e.g., 10 lbs to 11 lbs vs. 100 lbs to 101 lbs).

Weber's Law

  • Formula: racriangleII=krac{ riangle I}{I} = k

    • Where $ riangle I $ (delta I) is the difference threshold,

    • $ I $ is the initial stimulus intensity, and

    • $ k $ is a constant that remains unchanged with varying $ I $ values.

Psychological Influences on Perception

Top-Down Processing

  • Definition: Perception is influenced by expectations and prior knowledge.

Bottom-Up Processing

  • Definition: Perception is constructed from individual bits of sensory information to form a coherent image.

Signal Detection Theory

  • Overview: Responses to stimuli depend on a person's sensitivity and decision criteria which can be influenced by multiple factors such as experience, expectations, motivation, and fatigue.

    • Outcomes:

    • Hit: Correctly identifying the presence of a stimulus.

    • Miss: Failing to detect a present stimulus.

    • False Alarm: Incorrectly identifying a stimulus as present.

    • Correct Rejection: Accurately identifying an absence of a stimulus.

Sensory Adaptation

  • Definition: Diminished sensitivity as a result of constant or recurring stimuli.

    • Examples: Not noticing the constant sound of an air conditioner or the feel of a watch on the wrist.

Attention and Inattentional Blindness

  • Definition:

    • Selective Attention: Focusing on one specific task while ignoring others.

    • Inattentional Blindness: A failure to perceive objects not focused on, exemplified by the gorilla suit experiment where participants miss seeing the gorilla while counting passes.

Change Blindness

  • Definition: The failure to notice changes in visual details of a scene.

  • Example: Observational changes in a film scene that viewers fail to detect.

The 5 Senses

Vision

  • Functionality: Light enters through the cornea and pupil, focused by the lens onto the retina, where an inverted image is projected.

  • Photoreceptors: Composed primarily of rods and cones within the retina.

    • Rods: 120 million, high sensitivity in dim light, low detail and color sensitivity.

    • Cones: 6 million, high color sensitivity and detail in bright light.

  • Color Vision:

    • Trichromatic Theory: Based on three types of cones sensitive to different wavelengths (short, medium, long).

    • Opponent-Process Theory: Color perception occurs through opposing pairs (red-green, yellow-blue, and black-white).

Visual Processing

  • Processing Pathways: Visual information is passed through the optic nerve and thalamus into the primary visual cortex where feature detectors respond selectively to specific features in the image.

  • Dorsal Pathway: Involved in the "where" aspect of processing visual information related to spatial awareness and movement.

  • Ventral Pathway: Important for object and face recognition but can lead to visual agnosia (difficulty processing objects) or prosopagnosia (difficulty recognizing faces).

Depth Perception

  • Monocular Cues: Perceived depth through one eye (e.g., relative size, height, and linear perspective).

  • Binocular Cues: Require both eyes—retinal disparity is the slight difference in images received from each eye, and convergence occurs when eyes turn inward to focus on closer objects.

Perceptual Constancies

  • Size Constancy: Keeping the perceived size of objects consistent even when viewed from different distances.

  • Brightness Constancy: Perceiving a constant color even when lighting conditions change.

Audition (Hearing)

  • Components: Involves the outer ear (pinna), middle ear (ossicles), and inner ear (cochlea).

  • Sound Localization: The ability to locate the source of a sound which relies on differences in sound arrival times to each ear.

  • Multimodal Integration: Interaction of multiple sensory systems to enhance perception of objects/events.

    • Synesthesia: A condition where stimulation in one sensory modality evokes sensations in another (e.g., hearing colors).

Conclusion

  • Understanding sensation and perception is essential for comprehending how we interact with our environment and how our sensory systems affect our interpretation of the world.