PSY 102: Sensation and Perception

PSY 102: Introduction to Psychology I

• This course is being held in the Winter of 2025 by instructor Professor Margot Sullivan (she/her)
• Students can raise their hand during class to ask a question
• Students can speak with the professor during breaks
• Poll Everywhere can be accessed via a link or QR code on a phone or laptop
• Poll Everywhere is ungraded and anonymous
• Registration is not required for Poll Everywhere; students can press skip

Lecture 5: Sensation and Perception

• Lecture 5 focuses on sensation and perception

Sensation vs. Perception

• Sensation and perception are the topic of the lecture

Demo: Image in the Distance?

• People can have different perceptions of what is in the image in the distance
• The object in the picture could be driftwood, a rock, an umbrella or a computer

What is Sensation and Perception?

• Sensation is the detection of physical energy by the sense receptors
• Perception is the brain's interpretation of raw sensory data

Sensation

• Raw data is processed by sensory receptors, eg. eyes, ears, nose, skin and tongue

Perception

• Sensations are processed in the brain

Ebbinghaus-Titchener Illusion

• Perceptual illusions happens when perception of a stimulus does not match its physical reality
• Example of perceptual illusion is the Ebbinghaus-Titchener Illusion
• Context plays a key role in illusions

Brains Filling in Context

• Our brains fill in context when perceiving things
• The brains fill in missing information

Primary Visual Cortex (V1)

• Non-existent triangle activates the primary visual cortex (V1)

Transduction

• The nervous system converts an external stimulus into electrical activity within neurons through transduction.
• A specialized cell called the sense receptor performs transduction.

Doctrine of Specific Nerve Energies

• Sensations experienced are determined by the nature of the sense receptor, not the stimulus.
• Phosphenes are sensations of light caused by pressure on the eye's receptor cells.

Sensory Adaptation

• Activation is highest when a stimulus is detected for the first time.
• Over time smells, sounds, touch, and taste decrease.

Psychophysics

• Psychophysics, created by Gustav Fechner in 1860, is the study of how we perceive sensory stimuli based on their physical characteristics

Absolute Threshold

• Absolute Threshold is the lowest level of a stimulus needed for a person to detect that stimulus 50% of the time.

Just Noticeable Difference (JND)

• Smallest change in the intensity of a stimulus that humans can detect.
• Weber's Law suggests a constant proportional relationship between the JND and the original stimulus intensity.
• Stronger stimuli result in a higher JND, and lower stimuli result in a lower JND.

Cross-Talk Between Senses

• Cross-modal processing can influence perception
• McGurk Effect demonstrates how we integrate visual and auditory information. eg. Hear "ba", See "ga", Perceive "da"

Synesthesia

• Synesthesia is where people experience cross-modal sensations.
• The most common form of synesthesia is grapheme-color synesthesia -During these experiences, parts of the visual cortex become active.
• Lexical-taste synesthesia is where words have tastes.

Role of Attention

• Selective attention is the process of selecting one sensory channel and ignoring/minimizing others.
• The reticular activating system (RAS) in the reticular formation plays a role.
• A network of regions in the cerebral cortex also plays a role.

Broadbent's Filter Theory of Attention

• The Dichotic Listening Task involves playing two different messages one to each ear.
• The ignored message is not processed well.

Filter Theory of Attention

• Anne Treisman's (1960) Filter Theory states that filter is more complex than "On” vs. “Off”.
• Shadowing involves repeating the attended message.
• There is a "leaky filter" based on meaning and the message is processed at some level.

Cocktail Party Effect

• People become aware of stimuli outside of our attention when it is relevant, such as hearing your name.

Inattentional blindness

• People are poor at detecting stimuli in plain sight if focus is elsewhere.

Change Blindness

• Change blindness is the failure to detect changes in your environment. It causes continuity errors in movies and TV shows.

The Visual System

• Light is a form of electromagnetic energy.
• Humans respond to a narrow spectrum of light and bees respond to 300 to 650 nm.

Colour

• Brightness is the amount of light reflected back to the eye.
• Hue is the colour of light.

Structure of the Eye

• The iris controls how much light enters the eye.
• The pupil is the hole where light enters the eye.
• Pupillary reflex is a response to bright light and pupil dilation occurs when processing complex information with autonomic arousal

Cornea

• Transparent cells that focus light on the back of the eye.

Lens

• Keeps images in focus & changes curvature (accommodation) to reflect light onto back of eye

Retina

• Membrane at the back of the eye that contains rods and cones
• Cones are in the detail and enable for High light requirement, colour vision
• Rods are in the shapes and forms and enable Low-light vision, dark adaptation and are Absent in fovea

Pathway of Vision

• Optic Nerves > Optic Chasm > Optic Tract > Thalamus > Optic Radiations > Primary Visual Cortex (V1)

Feature Detectors

• Hubel & Wiesel (1960s) researched feature detectors with visual stimuli in cats
• Visual cortex (V1) = early stage of visual processing.
• Feature detectors are neurons that respond best to a specific stimulus.

Trichromatic Theory

• According to this theory, colour vision is based on three primary colours: blue, green, and red, and is consistent with cone types.
• It explains colour blindness

Opponent Process Theory

• Colour perception theory is where one theory is where colour vision is when one member of the colour pair suppresses the other colour and Accounts for afterimages.

Hearing

• Sound is vibration with physical properties
• Pitch is measured in wave frequency (Hz); we perceive a range of 20 to 20,000 Hz
• Loudness is measured in amplitude of the sound waves (dB)

The Ear Structures

• Outer part Includes the pinna and ear canal.
• Middle part Ossicles vibrate and transmit sound to the inner ear.

Cochlea

• The cochlea converts vibration into neural activity based on pitch perception.
• It contains the Organ of Corti and basilar membrane and hair cells.

Smell and Taste

• Olfaction (smell) and gustation (taste) work hand in hand.
• Smell and taste are described as the "chemical senses."
• Odours are airborne chemicals that interact with lining in nasal passages.
• Humans are sensitive to 2000 to 4000 different odours.
• People are sensitive to five basic tastes: Sweet, salty, sour, bitter, umami

Taste Receptors

• The tongue contains taste buds for each taste.

Somatosensory System

• Touch and pain involves specialized nerve endings in the skin (mechanoreceptors).
• It Responds to stimuli applied to skin, touch, pressure, temperature, and injury.
• Low-intensity stimulus has slow firing
• High-intensity stimulus has fast firing
• Rate is related to stimulus intensity which is related to our experience.

Bottom-up processing

• Bottom-up processing relies on sensory data alone.
• In bottom up process Whole stimulus is constructed from the parts. Raw stimulus goes in the direction to sensory system which in turn goes to Brain which then produces meaningful concepts

Top-down processing

• Top-down processing is a process where Raw stimulus is modified by experiences, knowledge, expectations/beliefs, and goals.
• In top down processing, brain (meaningful concepts) -> sensory processing of raw stimulus

Gestalt Principles of Object Perception

• Rules that govern how perceive objects as wholes within their overall context such as Proximity, Similarity, Continuity, Closure, Symmetry and Figure-ground

Hearing

• To determine motion, the brain compares visual frames of what is to what was.
• Phi phenomenon: successive flashing of lights = movement.

Depth Perception

• Ability to see spatial relations in three-dimensions.
• Monocular depth cues rely on one eye that include relative size, texture gradient and interposition
• Binocular depth cues require both eyes and includes disparity and convergence
• Experiment in the visual cliff has found that visual perception is innate and learned.