Sensation and Perception Chalalai taesilapasathit Faculty of liberal arts, Thammasat university

Key terms Sensation: Activation of the sense organs by a source of physical energy Perception: The process of organizing and interpreting sensory information Stimulus: Energy that produces a response in a sense organ Psychophysics: Study of the relationship between physical aspects of stimuli and our psychological experience of them

Sensation and Perception Unified Information Processing System Bottom-up Processing Initiated by sensory input Outside world’s influence on perception Top-down Processing Initiated by cognitive processing Internal/mental world’s influence on perception Expectations & prior understanding

Sensation Sensory receptors: Specialized cells that selectively detect and transmit sensory information to the brain Cells send signals via distinct neural pathways

Sensation Photoreception vision Mechanoreception touch Chemoreception Smell and taste

Sensory Thresholds A threshold is an edge, a boundary. Absolute threshold: Detecting what’s out there Smallest intensity of a stimulus that must be presented for it to be detected The stimulus intensity that is detected 50% of the time Noise-background stimulation that interferes with the perception of other stimuli Unwanted stimuli that interfere with other senses

Sensory Thresholds Difference threshold: Noticing distinctions between stimuli Smallest level of added or reduced stimulation Required to sense that a change in stimulation has occurred Also called a ‘just noticeable difference’ Just Noticeable Difference (JND) JND increases with stimulus magnitude An increase in JND is a decrease in sensitivity

Sensory Threshold Weber’s law: A basic law of psychophysics To be perceived as different, two stimuli must differ by a constant minimum percentage (not a constant amount)

(McGraw-Hill Education)

Subliminal Perception Influence of information below the level of conscious awareness The study by James Vicary, the Popcorn Experiment

Signal Detection Theory Decision “Did I detect something?” Information acquisition Criterion (basis, motive for judgement) Whether we can tell that something is there depends on much more than how sensitive our receptors are.

Stroop Effect As fast as you can, name each color of ink used to print each of the rectangles below.

Stroop Effect As fast as you can, name the color of ink used to print each word shown below, ignoring what each word says.

Factors Affecting Perception Attention Perceptual Set Sensory Adaptation Focusing awareness on a narrowed aspect of the environment Selective attention Cocktail party effect Stroop effect Emotion-induced blindness Inattentional blindness Predisposition or readiness to perceive something in a particular way Change in responsiveness of sensory system Based on level of surrounding stimulation (darkened room, bright outdoors)

Extrasensory Perception Perceive thoughts or events in the absence of concrete sensory input Parapsychology Problematic for science What type of energy encodes that information? By what receptors is the information received? Total lack of supportive research evidence Stories/experiences that seem to support ESP not rigorous

Visual Perception Properties of light: Wavelength (distance between peaks) Perceived as hue Some wavelengths beyond human sensation Amplitude (height of wave) Perceived as brightness Purity (mixture of wavelengths) Perceived as saturation

Structure of the Eye: Retina Photo-Receptor Cells Rods: Sensitive to even dim light, but not color Function well in low illumination Humans have approx. 120 million rods Cones Respond to color Operate best under high illumination Humans have approx. 6 million cones

Fovea: Densely populated with cones vital to many visual tasks Blind Spot FOVEA Optic Nerve Blind spot: where the optic nerve leaves the eyeball Ganglion Cells Bipolar Cells © McGraw-Hill Education Permission required for reproduction or display

From the Eye to the Brain When light strikes the retina: Stimulation of the nerve cells triggers a neural response Reaches the rods Receive information directly from the rods and cones Bipolar cells Collect and summarize visual information Ganglion cells Carries visual information to the brain Optic nerve

Pathway of Visual Information Left Visual Field Right Visual Field Pathway of Visual Information Retina Optic Nerve Optic Chiasm: optic nerve fibers divide Left Hemisphere Right Hemisphere Thalamus Visual Cortex © McGraw-Hill Education Permission required for reproduction or display © RubberBall Productions/Getty Images RF

Theories of Color Vision Trichromatic theory Suggesting that there are three kinds of cones in the retina, each of which responds primarily to a specific range of wavelengths Additional evidence from some types of color deficiency or color blindness Color blindness  One or more types is inoperative Opponent-process theory Receptor cells are linked in pairs, working in opposition to each other Color afterimages  occur because activity in the retina continues even when you are no longer staring at the original picture Trichromatic theory cannot explain afterimages

Note: Direct students to stare at this image for 25-30 seconds, then switch quickly to the center of the gray square. © McGraw-Hill Education Permission required for reproduction or display

Opponent-Process theory

Visual Perception Organizing and interpreting visual signals Dimensions: Shape Depth Motion Constancy

Gestalt Psychology Perceptions are naturally organized according to certain patterns Gestalt principles: Figure-ground relationship Closure Proximity Similarity

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Closure Proximity Similarity Note the rows and columns being different in Similarity. Similarity © McGraw-Hill Education Permission required for reproduction or display

Visual Perception: Depth The brain constructs perception of 3D from 2D images processed by the retina Binocular cues: Disparity Convergence Monocular cues: Familiar size, overlap Shading, texture gradients Height in field, linear perspective

Hearing Perception Properties of sound: Wavelength (distance between peaks) Determines frequency Perceived as pitch Some wavelengths cannot be perceived Amplitude (height of wave) Perceived as loudness Mixture of wavelengths (complex sounds) Perceived as timbre/tone saturation

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Place Theory of Pitch Perception Frequency Theory of Pitch Perception Theories of Hearing Place Theory of Pitch Perception Location of stimulation is important Only explains perception of high frequencies Frequency Theory of Pitch Perception Frequency of nerve firing Limitations of neuronal firing rate Volley principle Cell clusters can exceed limitations of firing rate

Cochlea  Auditory nerve  Brain stem  Temporal lobe Auditory Processing Pathway of auditory information Cochlea  Auditory nerve  Brain stem  Temporal lobe Most information crosses to other hemisphere Localizing sound Intensity (distance, sound shadow) Timing

Other Senses: Smell Olfaction Sense of smell is sparked when the molecules of a substance enter the nasal passages Olfactory cells  Receptor neurons of the nose Pheromones  Chemicals secreted into the environment  Produce a reaction in other members of the same species

Other Senses: Taste Gustation (Sense of taste) Respond to basic stimulus qualities: Sweet Sour Salty Bitter “Umami” Taste buds: Supertasters  highly sensitive to taste Nontasters  insensitive to taste

Other Senses: Skin Skin senses: Touch, pressure, temperature, and pain Operate through nerve receptor cells located at various depths throughout the skin Pain-extensively researched skin sense Susceptibility to pain is different from person to person Substance P – transmits pain messages to the brain Gate-control theory of pain: Particular nerve receptors in the spinal cord lead to specific areas of the brain related to pain

Sensation and Social Psychology Empathy (Feeling what others are feeling) “feeling” refers here to emotions and perspectives Put yourself into someone’s shoes MTS (Mirror-Touch-Synesthesia): Tactile sensation phenomena Feeling what you see another person feel Doesn’t happen when they see a non-person touched