Sensation and Perception

Sensation and Perception

1. Psychophysics: Basic Concepts and Issues

   • Thresholds: Looking for Limits. Threshold is a dividing point between energy levels that do and do not have a detectable effect.
     • Absolute threshold: for a specific type of sensory input is the minimum amount of stimulation that an organism can detect, for example certain sound waves cannot be heard by the human ear.
   • Signal-Detection Theory: proposes that the detection of stimuli involves decision processes as well as sensory processes which are both influenced by a variety of factors besides stimulus intensity
   • Perception without Awareness: Subliminal perception is the registration of sensory input without conscious awareness.
   • Sensory Adaptation: is a gradual decline in sensitivity due to prolonged stimulation. eg constant loud music

2. Our Sense of Sight: The Visual System

   • For people to see, the stimulus is "light", an electromagnetic radiation that travels in a wave.
     • Amplitude is the height of the wave, mainly responsible for brightness.
       • Wave Length is the distance between peaks of light waves, and is mainly responsible for colour.
   • The Eye serves two purposes: channel light to the neural tissues that receives it and the eye also houses that tissue.
     • LENS: transparent eye structure that focusses the light rays falling on the retina
       • The PUPIL is the opening in the center of the iris that helps regulate the amount of light passing into the rear chamber of the eye.
   • Goodale and Humphrey 2001
     • Vision for Perception: allows you to build a model in your head of the external world eg seeing where a cat is sleeping
       • Vision for Action: process of controlling your actions that are directed at the objects you see eg petting the sleeping cat
   • RETINA: Neural tissue lining the inside back surface of the eye. it absorbs light, processes images, and sends visual information to the brain.
   • Viewing the World in Colour
     • Subtractive colour mixing works by removing some wavelengths of light, leaving less light than was originally there.
       • Additive colour mixing works by superimposing lights, putting more light in the mixture than exists n any one light by itself.
         • Trichromatic Theory of Colour Vision: the human eye has three types of receptors with different sensitivities to different light wavelengths. the three receptors are associated with the three primary colours of red, green, and blue. these three colours combine so you can see all other colours.
           • Colour Blindness: deficiency in the ability to distinguish between colours
             • Opponent Process Theory of Colour Vision: colour perception depends on receptors that make antagonistic response to three pairs of colours. (black vs white, red vs green, yellow vs blue)
   • Light falls on the eye but visual input is processed by the brain through neurotransmitters from the retina.

3. Our Other Senses

   • Kinesthetic System: monitors the position of the body's various parts
   • Vestibular system: responds to gravity and keeps you informed of your body's location space (balance and equilibrium). Cerebellum is critical to this.

4. Our Sense of Touch: Sensory Systems in the Skin

   • Gate-control theory: holds that incoming pain sensations must pass through a gate in the spinal cord that can be losed, thus blocking ascending pain signals
   • The skin houses many types of sensory receptors. they respond to pressure, temperature and pain. Tactile localization depends on receptive fields similar to those for vision.
   • Pain signals are sent to the brain along two pathways that are characterized as fast and slow. the perception of pain is highly subjective and maybe influenced by mood and distractions.

5. The Visual System: Perceptual Processes

   • Perceptual Set - A readiness to perceive a stimulus in a particular way. The same visual input can result in radically diferent perceptions because people interpret sensroy input differently, based on their expectations.
     • Feature Analysis: The process of detecting specific elements in visual input and assembling them into a more complex form. It assumes bottom up processing, progression from individual elements into the whole object. Top down processing is a progression from the whole to the elements.
       • Subjective contours is the perception of contoyrs or lines where none actually exist.
   • Gestalt Principles. Gestalt is another word for form or shape. came from Gestlat psychology with promoted that the whole can be greter than the sum of its parts. Top down processing. the visual scene is broken down into discrete forms.
     • Phi Phenomenon: the illusion of movement created by presenting visual stimuli in rapid succession eg a movie which is separate still pictures projected rapidly one after the other but as a whole it shows motion which you cannot see in the individual photos.
     • Figure (the thing being looked at) and ground (the background against which the figure stands)
       • proximity (nearness)
         • Closure - your eye completes figures that might actually have gaps in them
           • Similarity
             • Simplicity: people tend to group elements that form a good figure
   • Perceptual Hypothesis: an inference about which distal stimuli can be responsible for the proximal stimuli sensed
     • Distal stimuli - stimuli that lie in the distance (the objects outside the body that you are looking at))
       • Proximal stimuli - the stimulus energies that impinge directly on sensory receptors ie the energies that recpresent the objects you see.
         • Depth Perception: interpretation of visual cues that indicate how near or far away objects are
           • Binocular clues - distance based on differing views of two eyes
             • Monocular depth cues based on the image in either eye alone (one eye only)
               • perceptual constancy: tendency to experience a stable perception in the face of constantly changing sensory input
                 • Optical Illusion: an apparently unexplainable discrepancy between the appearance of a visual stimulus and its physical reality.

6. Our Sense of Hearing: The Auditory System

   • sound varies in terms of wavelength, amplitude and purity. these properties affect properties of pitch, loudness, and timbre respectively.
     • Sound is transmitted through the external ear via air conduction to the middle ear, where sound waves are translated into the vibration of tiny bones called ossicles (anvil, hammer and stirrup)
       • Place Theory proposed that pitch perception depends on where vibrations occur along the basilar membrane. Frequency Theory countered with the idea that pitch perception depends on the rate at which the basilar membrane vibrates.
         • Cochlea: fluid filled coiled tunnel that contains the receptors for hearing
           • Basilar Membrane: runs the length of the spiralled cochlea and holds the auditory receptors
             • Auditory receptors are called hair cells, because of the tiny bundles of hair that protrude from them

7. Our Chemical Senses: Taste (the gustatory system) and Smell (the olfactory system)

   • the taste buds are sensitive to four basic tastes: sweet, sour, bitter and salty
   • Taste preferences are largely learned or heavily influenced by one's cultural background
   • Smell is a chemical sense. Chemical stimuli activiate receptors called olfactory cilia which line the nasal pasages in the nose.
   • Pheromones: chemical messages typically imperceptible, that can be sent by one organism and received by another member of the same species.

8. Synesthesia: condition in which perceptual or cognitive activities trigger exceptional experiences

9. Perception: Selection, organization and interpretation of sensory input

10. Sensation: stimulation of sense organs

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