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Jim Mc Cutcheon

10/27/2013 8:30:00 AM http://www.ted.com/talks/iain_mcgilchrist_the_divided_brain.html Sensation The detection of physical energy emitted or reflected by physical objects Occurs when energy in the external environment or the body stimulates receptors in the sense organs Perception Process by which the brain organizes and interprets sensory information Sense Receptors Specialized cells that convert physical energy in the environment or the body to electrical energy that can be transmitted as nerve impulses to the brain Dendrites of sensory neurons responsible for smell, pressure, pain, and temperature Specialized cells for vision, hearing, taste Separate Sensations? Doctrine of specific nerve energies (Müller) Principle that different sensory modalities exist because signals received by the sense organs stimulate different nerve pathways leading to different areas of the brain If possible, allows for sensory substitution Sensory crossover also occurs in synesthesia where stimulation of one sense consistently evokes a sensation in another Colour purple smells like a rose http://www.youtube.com/watch?v=I0lmSYP7OcM Measuring the Senses Psychophysics Field concerned with the physical properties of stimuli are related to our psychological experience of them Commonly relies on measuring absolute threshold, difference, and applying signal-detection theory Absolute threshold The smallest quantity of physical energy that can be reliably detected by an observer (50% of the time) Senses are sharp, but only tuned into narrow band of physical energies Difference threshold The smallest difference in stimulation that can reliably be detected by an observer when two stimuli are compared Also called the just noticeable difference (JND) Weber’s law: size of JND proportional to size of initial stimulus JND for weight is 1/30 Also 50% of time Signal Detection Theory Divides the detection of sensory into a sensory process and a decision process False alarm is type 1 error (false positive) Miss is type 2 error (false negative) Sensory Adaptation and Deprivation Sensory adaptation Reduction or disappearance of sensory responsiveness when stimulation is unchanging or repetitious Useful as it spares us from responding to unimportant information Sensory deprivation The absence of normal levels of sensory stimulation Varied responses somewhat dependent on expectations and interpretations (e.g., hallucinations) Sensing without perceiving Selective attention Focusing of attention on selected aspects of the environment and blocking out the others Inattentional blindness Failure to consciously perceive something you are looking at because you are not attending to it Man in gorilla man walks through ball passing game un noticed Vision: The Stimulus Light = electromagnetic radiation Amplitude: perception of brightness Wavelength: perception of colour Purity: mix of wavelengths Perception of saturation, or richness of colours Light stimuli (waves) have physical characteristics that affect three psychological dimensions of our visual world: 1. Hue – dimension of visual experience specified by colour names related to the wavelength of light 2. Brightness – dimension of visual experience related to the amount of light emitted from or reflected by an object related to amplitude of wavelength 3. Saturation – dimension of visual experience related to the complexity of light waves vividness of purity of colour An Eye on the World cornea: protects eye and bends light toward lens lens: focuses on objects by changing shape iris: controls amount of light that gets into eye pupil: widens or dilates to let in more light The Retinal Image Visual Receptors Retina Neural tissue lining the back the eyeballs’s interior, which contains the receptors for vision Rods: visual receptors that respond to dim light 120-125 million, concentrated in the periphery of the retina highly sensitive to light (used for night vision) Cones: visual receptors involved in colour vision 7-8 million, concentrated in the centre of the retina (fovea) low sensitivity (used for day vision) sensitive to colour We experience chemical changes in rods and cones when our eyes adjust fully to dim illumination (called dark adaptation) Retinal processing also involves ganglion cells Neurons in the retina that gather information from receptor cells (by way of intermediary bipolar cells) Axons from the optic nerve which leaves the eye at optic disk (location of blind spot) Vision is Not Like a Camera Visual processing is an active process and involves many types of cells in different brain regions Cortical cells respond to line of specific orientations, others respond to properties of shapes and arrangements (e.g., spirals, faces, greebles) Feature detector cells Cells in the visual cortex that are sensitive to specific features of the environment Constructing the Visual World We rely on various Gestalt principles to organize visual input Figure: item of interest that stands out from the rest of the environment Ground: environment or background Proximity: things that are near each other tend to be grouped together Closure: our brain tends to fill in the gaps in order to perceive complete forms Similarity: things that are alike in some way tend to be perceived as belonging together Continuity: lines and patterns tend to be perceived as continuing in time or space Simplicity: we tend to view things or make out objects in the simplest way possible Binocular Cues Binocular cues provide visual cues to depth or distance requiring two eyes Up to 15 meters distance Convergence: the turning inward of the eyes which occurs when they focus on a nearby object Retinal disparity: the slight difference in lateral separation between two objects as seen by the left eye and the right eye Monocular Cues Monocular cues are visual cues to depth or distance that can be used by one eye alone Objects that are farther away Light and shadow, interposition, motion parallax, linear perspective, relative size, relative clarity, and texture gradients Interposition: if one object is blocking another…the one being blocked is farther away. See pages 205-207 for description and images Perception of distance also affected by emotional factors Visual Constancies Another important
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