Chapter 5 – Sensation and Perception

Chapter 5 – Sensation and Perception - Chapter 5...

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Chapter 5 – Sensation and Perception Sensation – the stimulus-detection process by which our sense organs respond to and translate environmental stimuli into nerve impulses that are sent to the brain Perception – active process of organizing the stimulus input and giving it meaning Sensory Processes Stimulus detection – absolute threshold designated as the lowest intensity at which a stimulus can be detected 50% of the time Signal detection theory – concerned with the factors that influence sensory judgments o Decision criterion – standard of how certain a person must be that a stimulus is present before they will say they detect it o Increased rewards for noticing stimuli often results in lower detection thresholds o Increased danger/punishment for noticing stimuli often raises detection threshold Difference threshold – smallest difference between two stimuli that can be perceived 50% of the time (just noticeable difference – jnd) o Weber’s Law – to perceive a difference between two stimuli, one must differ by a constant ratio Value for weights = 1/50, therefore if 50 lbs. is lifted, increased weight will only be detected at 51 lbs. Smaller fraction = higher sensitivity Doesn’t apply to extremely high or low stimulation intensities Sensory adaptation – the diminishing sensitivity to an unchanging stimulus o Perception of stimuli will decrease if constantly present The Sensory Systems Vision The Human Eye o Light enters eye through cornea (transparent protective structure) o Pupil – adjustable opening that dilates or constricts to control amount of light entering o Iris – controls the pupil o Lens – elastic structure that becomes thinner to focus on distant objects and thicker to focus on nearby objects Image flippedrrrrrrrrr and reversed onto retina Ability to see clearly depends on lens’ ability to focus image onto retina Myopia (nearsightedness) – lens focuses image in front of retina Hyperopia (farsightedness) – lens focuses image behind retina o Retina – multi-layered tissue at rear of eyeball Photoreceptors: Rods and Cones o Retina covered in light-sensitive receptor cells o Rods – black and white receptors Function best in dim light o Cones – color receptors Function best in bright light o In humans, rods are everywhere except fovea (direct center of retina) Cones decrease in concentration distant from the fovea o Rods and cones send message to brain via two additional layers of cells
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Bipolar cells have synaptic connections with rods and cones Bipolar cells synapse with ganglion cells, whose axons form into optic nerve o Cones in the fovea each have private line to a single bipolar cell (unlike others, which have many rods/cones for each bipolar cell)
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  • Spring '09
  • Psychology, Color blindness

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