Sensation and Perception: The Distinction Sensation: stimulation of sense organs, detecting stimuli and converting them into signals detectable by the nervous system – absorbing energy from light by the eyes Perception: selection, organization, and interpretation of sensory input – translating the sensory input into something meaningful 3 4 1821 - 1894 Psychophysics • The study of how physical stimuli inﬂuence our perceptions • Pioneered (and named) by Gustav Fechner • Without sensation, there’s no perception • Studied thresholds, just noticeable difference 5 Threshold A physical stimulus will not affect our perception if it is not a strong enough stimulus to be detected by our sensory receptors. Sensation begins when a physical stimulus is strong enough to activate/excite receptors. Threshold – the necessary intensity (level) of a stimulus to be detected by a sense receptor 6 Absolute Threshold There isn’t a clear amount / dividing line for what intensity will or won’t be strong enough to activate a receptor. Absolute threshold – the lowest (minimum) stimulus intensity that is capable of being detected (triggering receptors) 50% of the time – differs for different organisms – light detection experiment 7 8 9 Just Noticeable Difference ( JND) (Difference Threshold) Difference Threshold – how much a stimulus has to change before a person can detect that there’s a difference Just Noticeable Difference - smallest difference detectable 10 Weber’s Law Ernst Weber (1795-1878) Weber’s law: size of JND proportional to size of initial stimulus Example: The louder your music, the larger an increase in volume it takes for you to notice the difference. If the music is low, it doesn’t need to get that much louder before you notice. 11 Signal-Detection Theory: Sensory processes + decision processes Response Bias: prone to risk OR risk averse There is no one way to detect what’s in front of you. You are constantly making judgments about perception. When perceptual event is ambiguous, response bias determines how it is interpreted. 12 Signal-Detection Theory 13 Selective Attention There are 11,000,000 pieces of sensory information coming in at any given moment. You pay attention to 40 of them. (Dual processing:your brain is still subconsciously processing the rest of the information.) Cocktail Party Effect - A person can pay attention to a single voice in a crowded room full of other talking people 14 Selective Attention The cognitive process of focusing on a particular object in the environment for a certain period of time. Attention is a limited resource, so selective attention allows us to tune out unimportant details and focus on what really matters. Inattentional blindness Change Blindness 17 Sensory Adaptation (Habituation) Decline in sensitivity to prolonged stimulation – a behavioral adaptation We adjust to the smell of strong perfume and get used to the stench of ﬁsh from the market. Our eyes adjust to the bright light when we walk out of a movie theater. 18 Perceptual Organization • How do we organize our sensations into meaningful perceptions? • Gestalt Psychology – Wertheimer – the whole is other than the sum of its parts* – gestalt is a German word that means “whole” – if you see a part, your brain ﬁlls in the rest, to see the whole • Ex.: Necker cube – These are really just eight circles, each with three white lines in them. Your brain “sees” the cube. 19 Read the lines below aloud. Ca y u rea t is? You a e not r adi g th s. W at ar ou rea in ? 20 21 23 Bottom-Up Processing Bottom-up processing is also known as "small chunk" processing and suggests that we attend to or perceive elements by starting with the smaller, more ﬁne details of that element and then building upward until we have a solid representation of it in our minds. Perceptual Sets Perceptual sets: readiness to perceive a stimulus in a particular way, depending on expectations/context 25