🗓 Unit 5
Sensation & Perception

PSYC 181 – Intro to Psych

Emma Marshall – Instructor

University of Nebraska-Lincoln

July 23, 2024

What you will learn

Learning Objectives

• Understand how perception emerges from sensation
• Explore the processes of detecting stimuli and constructing useful information
• Examine the integration of sensation and perception in creating experiences

Sensation & Perception

Sensation:

Detection of external stimuli and transmission to the brain

Perception:

Processing, organization, and interpretation of sensory signals

Work together to create experiences

How does perception emerge from sensation? Independent systems but operate through interrelated processes

• Work together to: detect stimuli construct useful information about world use this constructed information to guide or behavior and decisions

Bottom-up Processing

perception based on the physical features of the stimulus

Top-down Processing

Interpretation shaped by available knowledge, expectation, or past experiences

Sensory Coding

Sensory organs ➜ Sensory receptors ➜ Neural pathway ➜ Cortical regions

Sensory receptors

specialized neurons that respond to specific types of stimuli

Detection requires a certain amount of stimulus

Transduction

When sensory receptors detect a specific stimuli, they convert that energy into an action potential which is sent to the central nervous system. This is called transduction.

Perception researchers try to understand the limits of human perception How much of a stimulus is necessary for us to begin to perceive it

Sense organs are constantly perceiving stimuli Need a certain amount to become aware of it (sensory threshold)

Absolute Thresholds

Minimum intensity before you experience a sensation

For a stimulus to cause an action potential, it first has to be strong enough to be detected. Absolute threshold – minimum amount of stimulus energy that must be present for the stimulus to be detected 50% of the time. On a clear night, the most sensitive sensory cells in the eye can detect a candle flame 30 miles away. We are also able to receive messages presented below the threshold of conscious awareness which are known as subliminal messages. The stimulus causes an action potential but we are not consciously aware of it. Just noticeable difference (JND) –the minimum difference in stimuli required to detect a change or a difference between stimuli. Can change depending on the stimulus intensity. A cell phone lighting up in a dark movie theatre is more likely to be noticed than if it lights up in a brightly lit shopping mall. The brightness of the cell phone does not change, but the ability to detect the change in illumination does. The JND would be the minimum increase in brightness required for the change to be detected.

Sensory Coding

Transduction:

Conversion of sensory stimuli to neural signals

Transformation:

Transmission of electrical impulses to specific cortical regions

Sensory systems

Transduction ➜ Transformation

Vision

Hearing (audition)

Smell (olfaction)

Taste (gustation)

Touch (somatosensation)

Body Position (proprioception)

Movement (kinesthesia)

Pain (nociception)

Temperature (thermoception)

Balance (vestibular sense)

Sense Pathways

SENSE	STIMULI	RECEPTORS	PATHWAYS TO THE BRAIN
Vision	Light waves	Light-sensitive rods and cones in retina of eye	Optic nerve
Hearing	Sound waves	Pressure-sensitive hair cells in cochlea of inner ear	Auditory nerve
Taste	Molecules dissolved in fluid on the tongue	Cells in taste buds on the tongue	Portions of facial, glossopharyngeal, and vagus nerves
Smell	Molecules dissolved in fluid on membranes in the nose	Sensitive ends of olfactory mucous neurons in the mucous membranes	Olfactory nerve
Touch	Pressure on the skin	Sensitive ends of touch neurons in skin	Cranial nerves for touch above the neck, spinal nerves for touch elsewhere

Vision

Anatomy Of the Visual System

Light path: Cornea → Iris → Lens → Retina

Transmission: Ganglion cells → Optic nerve → Thalamus → Visual cortex

1. Light waves are transmitted across the cornea and enter through the pupil.
2. The pupil’s size is controlled by muscles that are connected to the iris (the colored part of the eye).
3. The light crosses the lens and is focused on the fovea, which is part of the retina. The fovea contains photoreceptors. Photoreceptors are connected to retinal ganglion cells. Axons from these cells exit through the back of the eye where they form the optic nerve. The optic nerve then carries the visual information to the brain. Blind spot – a point of no receptors, where information exits the eye, where we cannot respond to visual information

photoreceptors

Receptor cells: Rods (low light) and Cones (color, higher light)

Figure 5.11 The two types of photoreceptors are shown in this image. Rods are colored green and cones are blue.

Cones Phototopic (daytime) vision. Work best in bright light conditions. High-acuity color information. Located in the fovea. Rods Scotopic (nighttime) vision. Work best in low light conditions. High-sensitivity. Allows for low-acuity vision in dim light. Involved in the perception of movement in our peripheral vision. Located in the periphery of the retina.

Optic Chiasm

Optic nerve of each eye merges in x-shape

The optic nerve of each eye merges at the optic chiasm, an X-shaped structure just below the cerebral cortex. Information from the right visual field is sent to the left hemisphere and information from the left visual field is sent to the right hemisphere. This information is then sent to the occipital lobe for processing.

Visual Pathways

• The “WHAT” pathway:
  • recognition
  • identification
• The “where/how” pathway
  • localization
  • what to do

After being processed in the occipital lobe, visual information exits and goes through two different pathways.

Waves

amplitude and wavelength

wavelenth is directly related to frequency or number of waves

Visual and auditory stimuli both occur in the form of waves. Two physical properties of waves are amplitude and wavelength. The amplitude or height of a wave is measured from the peak to the trough. The wavelength is measured from peak to peak.

Wavelength is directly related to frequency. Frequency – number of waves that pass a given point in a given time period. Expressed in hertz (Hz). Longer wavelengths have lower frequencies and shorter wavelengths have higher frequencies.

This figure illustrates waves of differing wavelengths/frequencies. At the top of the figure, the red wave has a long wavelength/short frequency. Moving from top to bottom, the wavelengths decrease and frequencies increase.

Light waves

The visible spectrum is the portion of the electromagnetic spectrum that we can see. Different species can see different portions of the spectrum. Humans can see wavelengths ranging from about 380 – 740nm.

Perception of Color

Wavelength ➜ Color

• Longer wavelengths = reds
• Intermediate wavelengths = greens
• Shorter wavelengths = blues and violets

Amplitude ➜ brightness/intensity

• Larger amplitudes = brighter

Wavelength and Color Different wavelengths of light are associated with our perception of different colors. Longer wavelengths = reds Intermediate wavelengths = greens Shorter wavelengths = blues and violets Amplitude and Color The amplitude of light waves is associated with brightness/intensity of color. Larger amplitudes appear brighter.

Color Vision

• Trichromatic Theory: Combine red, green, and blue
• Opponent-Process Theory: Color coded in opponent pairs
  • Black – White
  • Yellow – Blue
  • Green – Red

Trichromatic Theory of Color Vision All colors can be produced by combining red, green, and blue. Applies to the retina where color vision is controlled by three types of cones.

Opponent-Process Theory Color is coded in opponent pairs. Black – white Yellow – blue Green – Red Some cells are excited by one of the opponent colors and are inhibited by the other. Applies to cells after the retina. Research has found that both theories are true but for different parts of the visual system.

This figure illustrates the different sensitivities for the three cone types found in a normal-sighted individual.

Opponent-Process Theory

Afterimage: continuation of a visual sensation after removal of stimulus

When staring at a colored stimulus, the color-parings of the opponent-process theory lead to a negative afterimage.

Stare at the white dot for 30–60 seconds and then move your eyes to a blank piece of white paper. What do you see?

Depth Perception

Our ability to perceive spatial relationships in 3-D

• Binocular cues: Use both eyes (e.g., binocular disparity)
• Monocular cues: Use one eye (e.g., linear perspective, interposition)

Hearing

Anatomy of the auditory system

• Outer: pinna and tympanic membrane
• Middle: the three ossicles: malleus, incus, and stapes
• Inner: cochlea and basilar membrane

Auditory transduction

1. Sound waves → Tympanic membrane
2. Ossicles movement → Cochlea
3. Hair cell stimulation → Neural impulses
4. Auditory nerve → Brain processing

Sound waves travel along the auditory canal and strike the tympanic membrane, causing it to vibrate. The vibration causes the 3 ossicles to move. This presses the stapes into the oval window of the cochlea. The fluid inside the cochlea begins to move, stimulating the hair cells (sensory receptors for sound) which become activated. The hair cells generate neural impulses that travel along the auditory nerve to the brain. Auditory information is sent to the inferior colliculus, then the medial geniculate nucleus of the thalamus and finally to the auditory cortex in the temporal lobe for processing.

Pitch Perception

Temporal Theory: Frequency coded by neuron activity level

Place Theory: Different basilar membrane portions sensitive to different frequencies

How does the auditory system differentiate among various pitches? Temporal Theory Frequency is coded by the activity level of a sensory neuron. Problem – the frequency of action potentials cannot account for the entire range that we are able to hear. There is a point at which a cell cannot fire any faster. Place Theory Different portions of the basilar membrane are sensitive to sounds of different frequencies. The base responds to high frequencies and the tip responds to low frequencies. Both theories explain different aspects of pitch perception. The rate of action potentials applies up to about 4000Hz but higher frequencies can only be encoded using place cues.

Sound Localization

• Monaural cues: One ear
• Binaural cues: Two ears (interaural level and timing differences)

Localizing sound involves the use of two cues: Monaural cues: One ear Each ear interacts with incoming sound waves differently. Binaural cues: Two ears Provide information on the location of sound along a horizontal axis. Relies on differences in patterns of vibration.

Interaural level difference – sound coming from one side of the body is more intense at the closest ear because of the attenuation of the sound wave as it passes through the head. Interaural timing difference – small difference in the time at which a given sound wave arrives at each ear.

Hearing Loss

Deafness

Congenital deafness

Conductive hearing loss

Sensorineural hearing loss

Deafness – the partial or complete inability to hear. Congenital deafness – deafness from birth. Conductive hearing loss: Associated with a failure in the vibration of the eardrum and/or movement of the ossicles. Deafness – the partial or complete inability to hear. Congenital deafness – deafness from birth. Conductive hearing loss: Associated with a failure in the vibration of the eardrum and/or movement of the ossicles. Can often be dealt with using hearing aids which amplify incoming sound waves to make vibration of the eardrum and movement of the ossicles more likely to occur. Can be caused by: Age Genetic predisposition Environmental effects – exposure to extreme noise, certain illnesses or damage due to toxins. Sensorineural hearing loss – failure to transmit neural signals from the cochlea to the brain. Can be caused by Meniere’s disease which results in degeneration of inner ear structures.

Can often be dealt with using hearing aids which amplify incoming sound waves to make vibration of the eardrum and movement of the ossicles more likely to occur. Can be caused by: Age Genetic predisposition Environmental effects – exposure to extreme noise, certain illnesses or damage due to toxins. Sensorineural hearing loss – failure to transmit neural signals from the cochlea to the brain. Can be caused by Meniere’s disease which results in degeneration of inner ear structures.

Other Senses

Gustation (Taste)

• Six basic tastes: Sweet, Salty, Sour, Bitter, Umami, fat
• Taste buds and receptor cells

Research demonstrates that we have about 6 groupings of taste: Sweet Salty Sour Bitter Umami – associated with a taste for monosodium glutamate. Some research suggests we possess a taste for the fatty content of food. Taste buds - groupings of taste receptor cells with hair-like extensions that protrude into the central pore of the taste bud. Have a life cycle of 10 days to 2 weeks. Transduction: Taste molecules bind to receptors and cause chemical changes within the sensory cell. These changes result in neural impulses being sent to the brain.

Olfaction (Smell)

• Odor molecules bind to receptors
• Signals sent to olfactory bulb and cortex

Olfactory receptor cells: Contain small hair-like extensions which serve as the site for odor molecules to interact with chemical receptors located on these extensions (Located in a mucous membrane at the top of the nose).

Transduction: Odor molecules bind to receptors. Chemical changes cause signals to be sent to the olfactory bulb (where the olfactory nerves begin). Information is sent to the limbic system and primary olfactory cortex.

Pheromones – chemical messages sent by another individual. Many species respond to pheromones sent by another individual. Usually communicate information about the reproductive status of a potential mate

Somatosensation

Touch

• Meisnerr’s corpuscles: respond to pressure and lower-frequency vibrations
• Pacinian corpuscles: detect transient pressure and higher-frequency vibrations
• Merkel’s disks: respond to light pressure
• Ruffini corpuscles: detect stretch

Thermoception: Temperature perception

Nociception: Pain perception

Pain Perception

Inflammatory pain vs. Neuropathic pain

As well as receptors located in the skin, there are a number of free nerve endings that have sensory functions. Thermoception – temperature perception Nociception – sensory signal indicating potential harm and maybe pain. This type of sensory information travels up the spinal cord directly to the brain, specifically the medulla, thalamus and the somatosensory cortex.

Inflammatory pain– signals some type of tissue damage. Neuropathic pain – caused by damage to neurons of either the peripheral or central nervous system.

Vestibular Sense

The vestibular system also collects information important for controlling movement and reflexes that move parts of our bodies to compensate for changes in body position.

Proprioception & kinesthesia

• Proprioception: Balance and body posture
• Kinesthesia: Perception of body position and movement

Both proprioception and kinesthesia interact with information provided by the vestibular system. Proprioception - perception of body position. Kinesthesia – perception of the body’s movement through space. This information travels to the brain via the spinal column. Information from the brain is then sent to the sensory organs of the proprioceptive and kinesthetic systems.

Perception Principles

Gestalt Principles

1. Figure-ground relationship
2. Proximity
3. Similarity
4. Continuity
5. Closure

Gestalt Principles of perception

Idea that the whole is different from the sum of its parts

Gestalt psychology – field of psychology based on the idea that the whole is different from the sum of its parts. The brain creates a perception that is more than simply the sum of available sensory inputs. The brain does this in predictable ways which gestalt psychologists translated into principles by which we organize sensory information. Principles include: Figure– ground relationship Proximity Similarity Continuity Closure

Figure-Ground relationship

• Figure: focus of visual field
• Ground: background

The idea that we tend to segment our visual world into figure and ground. Figure – the focus of the visual field. Ground – the background. Our perception can vary depending on what we view as figure and what we view as ground.

The concept of figure-ground relationship explains why this image can be perceived either as a vase or as a pair of faces.

Gestalt Principle of proximity

things that are close tend to be grouped together

Gestalt Principle of similarity

The idea that things that are alike tend to be grouped together

Gestalt Principle of continuity

more likely to percieve continuous, smoot flowing lines

The idea that we are more likely to perceive continuous, smooth flowing lines rather than jagged, broken lines.

Good continuation would suggest that we are more likely to perceive this as two overlapping lines, rather than four lines meeting in the center.

Gestalt Principle of Closure

look for complete objects rather than parts

The idea that we organize our perceptions into complete objects rather than as a series of parts.

Closure suggests that we will perceive a complete circle and rectangle rather than a series of segments.

Duck or Rabbit?

Factors Affecting Perception

• Sensory adaptation
• Attention (e.g., inattentional blindness)
• Motivation
• Beliefs, values, and expectations
• Cultural experiences

Sensory adaption – not perceiving stimuli that remain relatively constant over prolonged periods of time. For example, when you first enter a quiet room you may hear the clock ticking. Over time you become unaware of the ticking. The ticking is still affecting sensory receptors but you are no longer perceiving the sound. Attention Inattentional blindness - Failure to notice something that is completely visible because of a lack of attention. Nearly one third of participants in a study did not notice that a red cross passed on the screen because their attention was focused on the black or white figures.

Motivation Sometimes we think we hear something such as a phone ringing when it is not because we are motivated to perceive it (such as waiting for an important phone call). Signal detection theory – change in stimulus detection as a function of current mental state. Beliefs, values, prejudices and expectations People who hold positive attitudes towards low-fat foods are more likely to rate foods with low-fat labels as tasting better than people with less positive attitudes about low-fat products. Life/Cultural experiences One study found that people from Western cultures (where there is a perceptual context of buildings with straight lines) were more likely to experience certain types of visual illusions, like the Muller-Lyer illusion, than individuals from non-western cultures (where they are more likely to live in round huts).

Muller-Lyer Illusion

In the Müller-Lyer illusion, lines appear to be different lengths although they are identical. Arrows at the ends of lines may make the line on the right appear longer, although the lines are the same length. When applied to a three-dimensional image, the line on the right again may appear longer although both black lines are the same length.