Sensation and Perception: Foundations, Processes, and Influences

Sensation and Perception

Introduction to Sensation and Perception

Sensation and perception are fundamental processes in psychology that allow us to experience and interpret the world around us. Sensation refers to the detection of physical energy by sensory organs, while perception involves the brain's interpretation of this sensory data.

• Sensation: Detection of physical energy (stimuli) from the environment by sense organs.

• Perception: The process by which the brain organizes and interprets sensory information.

Transduction

Transduction is the process by which sensory receptors convert external stimuli into neural impulses that can be interpreted by the brain.

• Definition: Conversion of one form of energy into another.

• Process:

  • Receive sensory information via receptor cells.

  • Transform the stimulation into neural impulses (action potentials).

  • Deliver the neural information to the brain.

The Multisensory Brain

Perception is based on building simple input into more complex perceptions. The brain integrates information from multiple senses to form a coherent experience.

• Bottom-up processing: Perception based on incoming sensory information.

• Top-down processing: Perceptual processes in which memory and other cognitive processes are required for interpreting incoming sensory information.

Sensory Adaptation

Sensory adaptation refers to the process by which sensitivity to a constant stimulus decreases over time.

• Activation is highest at first detection, then adaptation occurs.

• Sensory receptor cells become less responsive to unchanging stimuli.

• Adaptive – conserve energy, focus on novelty and changes.

Psychophysics: Measurement of Sensation

Psychophysics studies the relationship between physical stimuli and the sensations and perceptions they produce.

• Absolute threshold: Minimum intensity of a stimulus that a person can detect half the time.

• Example: A candle 48 km away on a clear night, 1 tsp of sugar in 7.5 L of water.

• Noticeable difference (JND/Difference threshold): The degree of difference that must exist between two stimuli before the difference is detected.

• Weber's Law: JND between two stimuli is not absolute, but an amount relative to the magnitude of the stimuli. $\frac{\Delta I}{I} = k$

Subliminal Perception

Subliminal perception occurs when stimuli are presented below the threshold of conscious awareness.

• Perception of stimuli that are presented at a level below threshold.

• Limited practical application (e.g., self-help tapes).

Attention in Sensation and Perception

The Role of Attention

Attention is crucial for selecting relevant sensory information and filtering out distractions.

• Selective attention: Focusing on a specific aspect of sensory input while ignoring other stimuli.

• Attention as a bottleneck – other channels are still processed at some level.

Inattentional Blindness

Inattentional blindness is the failure to detect unexpected stimuli in plain sight when attention is focused elsewhere.

• Limited attentional resources, focus on what we deem important.

Change Blindness

Change blindness is the failure to notice changes in your environment, often due to distraction or limited attention.

• Limited resources further constrained by age, distraction, etc.

Illustrative Example: Officer Wrongfully Convicted for Missing 'the Obvious'

• Boston officer charged with misconduct for 'lying' claimed he did not see other officers beating a suspect as he ran past, chasing a murder suspect.

• Simulation study: subjects jogged behind experimenter who ran past simulated fight scene; 65% missed the fight at night, 44% during broad daylight.

Sensory Systems

Senses

Humans have several senses, each with specialized receptors and functions.

• Vision (visual)

• Sound (auditory)

• Hearing (auditory)

• Taste (gustatory)

• Touch (tactile)

• Balance & Movement (vestibular)

• Body awareness (proprioception)

Vision

Vision is the sense that detects light and interprets it as images.

• Retina: Light-sensitive back inner surface of eye; contains rods and cones.

• Optic nerve: Carries neural impulses from eye to brain.

• Blind spot: Point where optic nerve leaves the eye; no receptor cells.

The Eye: Vision's Window

• The eye adjusts to incoming light that enters the eye.

• Pupil size changes in response to light intensity and emotional states.

• Constriction signals disgust or refusal; dilation signals arousal.

Rods and Cones

Retinal receptors are specialized for different aspects of vision.

• Rods: Detect black, white, and gray; sensitive to movement; peripheral and twilight vision; low light situations; located in periphery.

• Cones: Sharp focus, color perception, detail; work well in daylight; clustered around fovea.

Colour Vision

Colour vision is explained by two main theories: trichromatic theory and opponent process theory.

• Trichromatic theory: Retina contains three types of cones (red, green, blue); consistent with three types of cones in eyes; explains colour blindness but not afterimages.

• Opponent process theory: Colours are perceived in terms of three pairs of opponent colours: red/green, blue/yellow, black/white.

Colour Constancy

Colour constancy is the ability to perceive an object as having the same colour under varying illumination conditions.

• Illusions can occur when this adjustment leads to misperception of colour.

Depth and Distance Perception

Depth perception allows us to judge the distance of objects. It relies on both monocular and binocular cues.

• Monocular cues: Require only one eye (e.g., relative size, texture gradient, overlap/occlusion, height in field of view, linear perspective, motion parallax).

• Binocular cues: Require both eyes (e.g., retinal disparity).

Hearing (Audition)

Sensing Sound

Hearing involves the detection of sound waves and their conversion into neural signals.

• Outer ear: Funnels sound toward ear drum.

• Eardrum: Vibrates when sound waves make contact; transmits vibrations to middle ear.

• Middle ear: Contains three tiny bones (stirrup, anvil, hammer) that act as mechanical amplifiers.

• Inner ear: Cochlea filled with fluid that vibrates in response to sound; hair cells detect vibrations and transmit neural messages.

• Basilar membrane: Runs through center of cochlea; divided into two chambers; covered with hair cells.

When We Can't Hear

• Conductive deafness: Malfunctioning of the ear, especially the failure of eardrum or ossicles.

• Nerve deafness: Due to damage to auditory nerve.

• Noise-induced hearing loss: Damage to hair cells due to repeated loud noises.

• Sudden sensorineural hearing loss: Sudden loss of hearing due to nerve damage.

Socio-cultural Influences on Auditory Perception

• Cultural and social life provide frameworks for interpretation of stimuli.

• Site wave sound experiments – what people hear depends on expectations.

Perception is Multisensory and Constructive

Multisensory Integration

The brain combines information from multiple senses to create a coherent perceptual experience.

• Brain builds a coherent experience from multiple sources (even if it results in an illusion).

• Example: The McGurk effect – visual information influences auditory perception.

The Multitasking Brain

• Begins with sensory receptors.

• We sense basic features of stimuli and integrate them.

Perceptual Organization

How We Organize Perceptions

We organize and interpret sights so they become meaningful perceptions. Perception is a constructive process, going beyond the stimuli presented to construct a meaningful situation.

• We don't passively respond to visual stimuli; we actively try to make sense of what we see.

• Recognition that objects are constant and unchanging even though sensory input about them is changing (size, distance, shape, colour).

• The moon appears larger when it is close to the horizon due to perceptual cues.

Context Effects on Perception

Expectations, context, and prior knowledge shape perception. We do not just see the world; we interpret it.

• Recall your own perceptions in different contexts (e.g., driver versus pedestrian).

• Context helps form perception and interpretation of a situation.

Emotions Can Sway Our Perceptions

Emotions influence how we interpret sensory information.

• Sad music predisposes us to perceive sad meanings (mourning vs. morning).

• Anger increases likelihood that neutral items will be mistaken as a weapon.

• Worrying about panic leads to interpreting physical sensations as panic.

Table: Comparison of Rods and Cones

Feature	Rods	Cones
Location	Periphery of retina	Clustered around fovea
Function	Detect black, white, gray; movement	Sharp focus; color perception; detail
Light Sensitivity	Low light (night vision)	Daylight (bright light)
Color Sensitivity	No color sensitivity	Color sensitive (red, green, blue)

Table: Theories of Colour Vision

Theory	Main Idea	Strengths	Limitations
Trichromatic Theory	Three types of cones (red, green, blue)	Explains colour blindness	Does not explain afterimages
Opponent Process Theory	Three pairs of opponent colours	Explains afterimages	Does not explain all aspects of colour vision

Additional info:

• Some content inferred from context and standard psychology curriculum (e.g., definitions, examples, and explanations of terms such as 'absolute threshold', 'Weber's Law', and 'McGurk effect').

• Tables reconstructed and expanded for clarity and completeness.