PYB102 Introduction to Psychology 1b Exam Revision Week 2 .doc

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Department
Psychology
Course
PYB102
Professor
Daniel S.Joyce
Semester
Spring

Description
PYB102 Introduction to Psychology 1b Week 2 Lecture Perception • perceptual psych. study the way we acquire info about the world via our various senses • bulk of perceptual research has been conducted in vision and audition domains Vision Light • for an object to be visible, it must emit or reflect light • The human eye is only capable of detecting light within a narrow range of wavelengths • Within this range of visible wavelengths, different wavelengths give rise to the perception of different colours Gross anatomy of the eye • The pupil changes in diameter (dilates) to accommodate changes in lighting Light is detected by receptors called rods and cones located at back of • retina • Schultze proposed that rods and cones form two separate visual systems (Duplex Retina Theory); • Photopic: Bright light vision via cones • Scotopic: Dim light vision via rods • Von Kries (1895) observed that individuals without rods were night blind. • The reverse applies for individuals without cones Normal colour vision in humans is trichomatic: Cones can contain either L (long), M (medium) or S (small). ← •All the colours which you can see are due to this combination of signalling by rods and cones •Some animals have more advanced colour vision than humans ← Colour deficiencies • Retinal "colour blindness" occurs in 8% of the male population (x-linked), <1% of females • Two main varieties: • anomaly of the photopigment (Altered spectral sensitivity) • deletion of the photopigment (dichromacy) • Protanopia – no L cones (red-green colour blind) Deuteranopia – no M cones (red-green colour blind) • • Tritanopia – no S cones (blue-yellow colour blind) Information Reduction Ganglion cell receptive fields • Each ganglion cell receives input from a number of adjacent receptor cells • These cells form the receptive field of the ganglion cell • Micro-electrode recordings indicate that many ganglion cells respond differently depending on whether the centre or the surround of their receptive field is illuminated • In some centre-surround receptive fields, illumination of the centre is excitatory while illumination of the surround is inhibitory. • This is called centre-surround antagonism The Visual Cortex • Optic nerve projects to the LGN, and then to the visual cortex in the occipital lobe at the rear of the brain • The VC is approximately 2 mm thick and contains ~100 million cells in 6 main layers with more complex behaviours • The LGN fibres enter layer IV, where the neurons have centre-surround receptive fields like those of ganglion cells • In other layers we find neurons with more complex behaviours Feature detectors in the visual cortex • Simple cortical cells respond to bars of a particular orientation • Complex cortical cells often respond best to a correctly oriented bar moving across the entire receptive field. Some cells are even direction sensitive • Hypercomplex cortical cells fire only to moving lines of a particular length or moving corners or angles • Summary: These cortical cells act as feature detectors Optical Illusions • The brain assumes that objects that are far away are bigger than they appear, therefore the top line appears longer than the bottom line. Blindsight • Rare condition in which a person lacks conscious perception of part or all of their visual field • Ability to detect, but not be aware of stimuli o Capacity to respond to visual information o Often expressed as a ‘feeling’ rather than a visual percept • Blindness is cortical (often in the VC) rather than from lower order processes (i.e., retina functions normally) • Behaviours are often automatic and informed by stimuli of which we can be completely unaware • Some people can experience blindsight just on one side of their vision The Stroop effect Interference of a reaction time task Conditions: no conflict vs conflict o Neutral, congruent, and incongruent o Reaction time (RT): incongruent> neutral> congruent Reading is an automatic task o Semantic meaning of the words takes priority o Semantic interference occurs when asked to name the incongruent colour of the text o Colour naming is not automated -> additional cognitive load required which increases RT o Semantic facilitation when asked to name the congruent colour of the text, RT decreases Taste • Sapid (tastable) substances must generally by water soluble • Most researches agree that there are four basic tastes: Sweet, Sour, Bitter, Salty • • Other researchers suggest metallic and unami (savoury) • These primary tastes are associated with substances w/ particular chemical properties Swe Generally associated with organic molecules like sugars & et alcohols. Many sweet substances (including non- organic ones) contain a component consisting of two negatively charged atoms and a positively charged hydrogen atom (AB,H system) Sour Generally associated with acids Bitte Often taste sweet in small amounts and often contain an AB,H r system many bitter substances contain nitrogen Salt Salty substances break into two electrically charged parts (ions) y when dissolved they size of the negative ion determines the saltiness (lighter = more salty) Overview of taste physiology Transduction of this chemical information into electrical signals occurs in taste buds: • Located in pits around papillae on the tongue, and on the soft palate • ~10000 taste buds, decreases with age • Taste buds contain a number (~50-150) of taste cells • Taste cells terminate in microvilli which project into the taste pore • Microvilli seem to be the site of reception for chemicals • Taste cells are replaced every few days • Nerve fibres exit from the back of the taste cells Models of taste coding Most taste receptors seem to respond to all 4 basic tastes, although with different sensitivities (Kimura & Beidler, 1961) • The cross-fiber patterning model (e.g., Pfaffman, 1955) argues that each substance we can taste generates a different pattern of activity across nerve fibres leading to different taste perceptions • Erickson (1963) noted that the pattern for potassium chloride and ammonium chloride are similar but that for sodium chloride is different; • Groups of rats fed one of these accompanied by an electric shock o KCl rats subsequently avoided NH4CL and visa versa, but the NaCl rats did not avoid either of the other 2 salts o Thus pattern of neural activity seems to correlate with taste The labelled-line theory (Pfaffman, 1974); • Assumes a best stimulus model of nerve fibre activity where specific fibres encode one of the four basic tastes depending on the one they respond
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