Chapter 5 – Sensation and Perception · Sensation – the stimulus-detection process by which our sense organs respond to andtranslate 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 presentbefore they will say they detect ito Increased rewards for noticing stimuli often results inlower 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 Eyeo Light enters eye through cornea (transparent protective structure)o Pupil – adjustable opening that dilates or constricts to control amount of lightentering o Iris – controls the pupilo Lens – elastic structure that becomes thinner to focus on distant objects and thicker to focus on nearby objects▪ Image flipped 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 Coneso 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 lighto In humans, rods are everywhere except fovea (direct center of retina) ▪ Cones decrease in concentration distant from the foveao Rods and cones send message to brain via two additional layers of cells ▪ 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)▪ Visual acuity (ability to see fine detail) increases with image directly on fovea o Blind spot exists at point where ganglion cells exit to form optic nerve ·
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- Winter '14