PSY 7: Biological Psychology Midterm 2

Chapter 6 The Visual System

What Do We See?

Somehow a distorted and upside-down 2-D retinal image is transformed into the 3-D world we perceive.

* Two types of research are needed to study vision.
* Research probing the components of the \n visual system
* Research assessing what we see

Light Enters the Eye and Reaches the Retina

No species can see in the dark, but some are capable of seeing when there is little light.

• Light can be thought of as:

  • Particles of energy (photons)

  • Waves of electromagnetic radiation

• Humans see light between 380–760 nanometers.

• Wavelength: perception of color

• Intensity: perception of brightness

The Pupil and the Lens

• Light enters the eye through the pupil, whose size changes in response to changes in illumination

• Sensitivity: the ability to see when light is dim

• Acuity: the ability to see details

• Lens: focuses light on the retina

• Ciliary muscles alter the shape of the lens as \n needed.

• Accommodation: the process of adjusting the \n lens to bring images into focus

Eye Position and Binocular Disparity

• Convergence: eyes must turn slightly inward when objects are close

• Binocular disparity: the difference between the images on the two retinas

• Both are greater when objects are close—together, they provide the brain with a 3-D image and distance information.

The Retina and Translation of \n Light into Neural Signals

• The retina is, in a sense, inside-out.

  • Light passes through several cell layers before reaching its receptors.

• Vertical pathway: receptors > bipolar cells > retinal ganglion cells

• Lateral Communication

  • Horizontal cells

  • Amacrine cells

• Blind spot: no receptors where information exits the eye

  • The visual system uses information from cells around the blind spot for “completion,” filling in the blind spot.

• Fovea: high-acuity area at center of retina

  • Thinning of the ganglion cell layer reduces distortion due to cells between the pupil and the retina.

Cone and Rod Vision

• Duplexity theory of vision: cones and rod mediate different kinds of vision.

• Cones: photopic (daytime) vision

  • High-acuity color information in good lighting

• Rods: scotopic (nighttime) vision

  • High-sensitivity, allowing for low-acuity vision in dim \n light, but lacks detail and color information

• There is more convergence in the rod system, \n increasing sensitivity while decreasing acuity.

• Only cones are found at the fovea.

Spectral Sensitivity

• Lights of the same intensity but different wavelengths may not all look equally bright.

• A spectral sensitivity curve shows the relationship between wavelength and brightness.

• There are different spectral sensitivity curves for photopic (cone) vision and scotopic (rod) vision.

Eye Movement

• We continually scan the world with small and quick eye movements: saccades.

• These bits of information are then integrated.

• Stabilize retinal image; see nothing

• The visual system responds to change.

Visual Transduction: The \n Conversion of Light to Neural \n Signals

• Transduction: conversion of one form of energy to another

• Visual transduction: conversion of light to neural signals by visual receptors

• Pigments absorb light.

• Absorption spectrum describes spectral sensitivity.Rhodopsin is the pigment found in rods.

• A G-protein-linked receptor that responds to light rather than to neurotransmitters.

• In the Dar

• Na+ channels remain partially open (partial depolarization), releasing glutamate.

• When Light Strike

• Na+ channels close

• Rods hyperpolarize, inhibiting glutamate release.

From Retina to Primary \n Visual Cortex

• The retinal-geniculate-striate pathways include \n about 90 percent of axons of retinal ganglion cells.

• The left hemiretina of each eye (right visual field) connects to the right lateral geniculate nucleus (LGN); the right hemiretina (left visual field) connects to the left LGN.

• Most LGN neurons that project to primary visual cortex (V1, striate cortex) terminate in the lower part of cortical layer IV.

Retinotopic Organization

• Information received at adjacent portions of the retina remains adjacent in the striate cortex (retinotopic).

• More cortex is devoted to areas of high acuity—like the disproportionate representation of sensitive body parts in somatosensory cortex.

• About 25 percent of primary visual cortex is dedicated to input from the fovea.

The M and P Channels

Magnocellular Layers (M Layers)

• Big cell bodies; bottom two layers of LGN

• Particularly responsive to movement

• Input primarily from rods

Parvocellular Layers (P Layers)

• Small cell bodies; top four layers of LGN

• Color, detail, and still or slow objects

• Input primarily from cones

• The channels project to slightly different areas in lower layer IV in striate cortex; M neurons are just above the P neurons.

• The channels project to different parts of visual cortex beyond V1.

Seeing Edges

Contrast Enhancement

• Mach bands: nonexistent stripes the visual system creates for contrast enhancement

• Makes edges easier to see

• A consequence of lateral inhibition

Receptive Fields of Visual Neurons

• The Area of the Visual Field within which It Is Possible for a Visual Stimulus to Influence the Firing of a Given Neuron

• Hubel and Wiesel looked at receptive fields in the retinal ganglion, LGN, and lower layer IV of striate cortex of a cat.

Receptive Fields: Neurons of \n the Retina-Geniculate-Striate \n System

Similarities seen at all three levels:

• Receptive fields of foveal areas are smaller than those in the periphery.

• Neurons’ receptive fields are circular in shape.

• Neurons are monocular.

• Many neurons at each level had receptive fields with excitatory and inhibitory area.

• Many cells have receptive fields with a center \n -surround organization: excitatory and inhibitory regions separated by a circular boundary.

• Some cells are on-center and some are off-center.

Receptive Fields: Simple and \n Complex Cortical Cells

• In lower layer IV of the striate cortex, neurons with circular receptive fields (as in retinal ganglion cells and LGN) are rare.

• Most neurons in V1 are either:

  • Simple—receptive fields are rectangular with “on” and “off” regions—or

  • Complex—also rectangular, with larger receptive fields, and respond best to a particular stimulus anywhere in their receptive fields

SIMPLE

• Rectangular

• “On” and “off” regions, like cells in layer IV

• Orientation and location sensitive

• All are monocular.

COMPLEX

• Rectangular

• Larger receptive fields

• Do not have static “on” and “off” regions

• Not location sensitive

• Motion sensitive

• Many are binocular.

Columnar Organization of \n Primary Visual Cortex

• Cells with simpler receptive fields send information on to cells with more complex receptive fields.

• Functional vertical columns exist such that all cells in a column have the same receptive field and ocular dominance.

• Ocular dominance columns: as you move horizontally, the dominance of the columns changes.

• Retinotopic organization is maintained.

Contextual Influences in Visual Processing

Plasticity appears to be a fundamental property of visual cortex function.

* E.g., receptive field properties depend on the scene in which the stimuli to its field are embedded.

Seeing Color: Component and \n Opponent Processing

Component Theory (Trichromatic Theory)

• Proposed by Young, refined by Helmholtz

• Three types of receptors, each with a different spectral sensitivity

Opponent-process theory was proposed by Hering.

• Two different classes of cells encoding color, and another class encoding brightness

• Each encodes two complementary color perceptions.

• This theory accounts for color afterimages and colors that cannot appear together (reddish green or bluish yellow).

Both theories are correct: coding of color by cones seems to operate on a purely component basis; opponent processing of color is seen at all subsequent levels.

Color Constancy and the \n Retinex Theory

Color constancy: color perception is not altered by \n varying reflected wavelengths.

• Retinex theory (Land): color is determined by the \n proportion of light of different wavelengths that a \n surface reflects.

• Relative wavelengths are constant, so perception is \n constant.

  • Dual-opponent color cells are sensitive to color contrast.

  • Found in cortical “blobs”

Cortical Mechanisms of Vision \n and Conscious Awareness

Flow of Visual Information

• Thalamic relay neurons, to

• 1 ̊ visual cortex (striate), to

• 2 ̊ visual cortex (prestriate), to

• Visual association cortex

As visual information flows through hierarchy, receptive fields:

• Become larger

• Respond to more complex and specific stimuli

Damage to Primary Visual \n Cortex

Scotomas

• Areas of blindness in contralateral visual field due to damage to primary visual cortex

• Detected by perimetry test \n

Completion

• Patients may be unaware of scotoma; missing details are supplied by “completion.”

Blindsight

• Response to visual stimuli outside conscious awareness of “seeing”

• Possible explanations of blindsight

  • Islands of functional cells within scotoma

  • Direct connections between subcortical structures and secondary visual cortex; not available to conscious awareness

Functional Areas of \n Secondary and Association \n Visual Cortex

• Neurons in each area respond to different visual cues, such as color, movement, or shape.

• Lesions of each area results in specific deficits.

• Anatomically distinct: about 12 functionally distinct areas have been identified so far.

• Retinotopically Organized

Dorsal and Ventral Streams

• Dorsal stream: pathway from primary visual cortex \n to dorsal prestriate cortex to posterior parietal \n cortex

  • The “where” pathway (location and movement), or

  • Pathway for the control of behavior (e.g., reaching)

• Ventral stream: pathway from primary visual cortex \n to ventral prestriate cortex to inferotemporal cortex

  • The “what” pathway (color and shape), or

  • Pathway for the conscious perception of objects

Prosopagnosia

Inability to Distinguish among Faces

• Most prosopagnosics’ recognition deficits are not limited to faces.

• Prosopagnosia is associated with damage to the ventral stream between the occipital and temporal lobes.

• Prosopagnosics may be able to recognize faces in the absence of conscious awareness.

• Prosopagnosics have different skin conductance responses to familiar faces compared to unfamiliar faces, even though they reported not recognizing any of the faces.

Akinetopsia

• Deficiency in the Ability to See Movement

• Progress in a Normal, Smooth Fashion

• Can Be Induced by a High Dose of Certain Antidepressants

• Associated with Damage to the Middle Temporal (MT) Area of the Cortex

Light enters the eye through the pupil, the hole in the ________.

iris

_____ is the ability to see the details of objects.

**Acuity**

Light reaches the ______ only after passing through the other four layers of neurons. Then, once the receptors have been activated, the neural message is transmitted back out through the retinal layers to the _________ cells.

receptor layer; retinal ganglion

_____ is the process whereby the receptor cells around the blind spot fill in the gaps in your retinal images.

Completion

_____ vision is cone mediated, predominates in _____ lighting, whereas _____ vision is rod mediated, and predominates in _____ lighting.

Photopic; good; scotopic; dim

Lights of the same intensity, but at different wavelengths, can vary widely in _____.

brightness

Which of the following is a kind of fixational eye movement?

Saccades

____________ is the conversion of light to neural signals by the visual receptors.

Visual transduction

All signals from the left visual field reach the right primary visual cortex, either ______ from the temporal hemiretina of the right eye or __________ (via the optic chiasm) from the nasal hemiretina of the left eye—and that the opposite is true of all signals from the right visual field.

ipsilaterally; contralaterally

The organization of the retina-geniculate-striate system is _____.

retinotopic

Two channels of parallel communication flow through the lateral geniculate nuclei. The _____ channel runs through the top four layers and the _____ channel runs through the bottom two layers of each lateral geniculate nucleus

parvocellular; magnocellular

The phenomenon of the perception of Mach bands is the result of _____.

lateral inhibition

“On-center” cells engage in “on-firing” _____.

when the central region of the receptive field is stimulated with light

Receptive fields in most primary visual cortex neurons fall into two classes_____, with neither class including the neurons of lower level IV.5

simple and complex

The primary visual cortex is organized into __________.

functional vertical columns

According to _______ theory, there are three different kinds of color receptors (cones), each with a different spectral sensitivity, and the color of a particular stimulus is presumed to be encoded by the ratio of activity in the three kinds of receptors.

component

The component theory of color vision was proposed by ________ in 1802 and refined by ________ in 1852.

Young; Helmholtz

Dual-opponent color cells are found in _____.

peglike blobs of the primary visual cortex

The primary visual cortex is located in the posterior region of the _____ lobes with much of it hidden from view by the _____ fissure.

 occipital; longitudinal

Persons with suspected damage to the primary visual cortex are given a _____ test indicating areas of blindness in each eye.

 perimetry

Blindsight is thought to result from damage to the _____ cortex.

primary visual

Most visual cortex neurons in the dorsal stream respond most robustly to ____________.

spatial stimuli

The inability to recognize faces is known as _____.

prosopagnosia

Prosopagnosia is often associated with damage to the _____.

 ventral stream and fusiform face area

Which of the following can trigger akinetopsia?

High doses of certain antidepressants

Chapter 7 Mechanisms of Perception: Hearing, Touch, Smell, Taste, and Attention

Principles of Sensory System Organization

Primary: input mainly from thalamic relay nuclei

• For example, the striate cortex receives input from the lateral geniculate nucleus.

• Secondary: input mainly from primary and secondary cortexes within the sensory system

• Association: input from more than one sensory system, usually from the secondary sensory cortex

Hierarchical Organization

• -→ Specificity and complexity increases with each \n level.

• -→ Sensation: detecting a stimulus

• -→ Perception: understanding the stimulus

• Functional segregation: distinct functional \n areas within a level

• Parallel processing: simultaneous analysis of \n signals along different pathways

Auditory System

• Natural sounds are complex patterns of vibrations.

• A Fourier analysis breaks natural sounds down into sine waves.

• There is a complex relationship between natural sounds and perceived frequency

The Ear

• Sound waves enter the auditory canal of the \n ear and then cause the tympanic membrane \n (the eardrum) to vibrate.

• This sets in motion the bones of the middleear—the ossicles—which trigger vibrations of the oval window.

• Sound Wave > Eardrum > Ossicles \n (Hammer, Anvil, Stirrup) > Oval Window

• Vibration of the oval window sets in motion the fluid of the cochlea.

• The cochlea’s internal membrane—the organ of Corti—is the auditory receptor organ

• The organ of Corti is composed of two membranes.

  • Basilar membrane: auditory receptors—hair cells \n —are mounted here.

  • Tectorial membrane: rests on the hair cells

• Stimulation of hair cells triggers action potentials in the auditory nerve.

Cochlear Coding

• Different frequencies produce maximal stimulation of hair cells at different pointsalong the basilar membrane.

• The basilar membrane and most other auditory system components are organized tonotopically—that is, by frequency

From the Ear to the Primary \n Auditory Cortex

• The axons of each auditory nerve synapse in the ipsilateral cochlear nuclei.

• From there, many projections lead to the superior \n olives on both sides of the brain stem.

• From there, axons project via the lateral lemniscus \n to the inferior colliculi.

• Axons then project from the inferior colliculi to the medial geniculate nuclei of the thalamus.

• Thalamic neurons then project to the primary auditory cortex

Subcortical Mechanisms of \n Sound Localization

The lateral and medial superior olives react to differences in what is heard by the two ears.

• Medial: differences in arrival

• Lateral: amplitude differences

Both project to the superior colliculus.

• The deep layers of the superior colliculus are laid out \n according to auditory space, allowing location of sound \n sources in the world; the shallow layers are laid out \n retinotopically.

Auditory Cortex

The auditory cortex is located in the temporal lobe.

• Core region: includes primary cortex

• The belt surrounds the core region

  • A band of secondary cortex

• Areas of the secondary cortex outside the belt are referred to as parabelt areas.

• About ten separate areas of secondary auditory cortex exist in primates

Organization of Primate \n Cortex

Functional columns: cells of a column respond to the same frequency

• Tonotopic Organization

• Secondary areas do not respond well to pure \n tones and have not been well researched.

What Sounds Should Be \n Used to Study Auditory \n Cortex?

There is a lack of understanding of the dimensions along which the auditory cortex evaluates sound.

• All through the cortical levels of the auditory system, there are cells that respond to complex sounds.

• Perhaps study with pure tones is limited

Two Streams of Auditory \n Cortex

Auditory signals are conducted to two areas of association cortex.

• -→ Prefrontal cortex

• -→ Posterior parietal cortex

• Anterior auditory pathway may be more involved in identifying sounds (what).

• Posterior auditory pathway may be more involved in locating sounds (where)

Auditory–Visual Interactions

• There is evidence for interactions between the auditory and visual systems.

  • E.g., some posterior parietal neurons with both visual and auditory receptive field

• Interaction in primary sensory cortices indicate that sensory system interaction is an early and integral part of sensory processing

Where Does the Perception \n of Pitch Occur

Most auditory neurons respond to changes in frequency rather than pitch.

* One small area just anterior to the primary auditory cortex has neurons that respond to pitch rather than frequency.
* This may be where frequencies of sound are converted to perception of pitch.

Effects of Damage to the \n Auditory System

Auditory cortex lesions in rats result in few \n permanent hearing deficits.

• Lesions in monkeys and humans hinder \n sound localization and pitch discrimination.

Deafness in Humans

• Total deafness is rare, due to multiple pathways.

• Two kinds: conductive deafness (damage to \n ossicles) and nerve deafness (damage to cochlea)

  • Partial cochlear damage results in loss of hearing at \n particular frequencies

Somatosensory System: \n Touch and Pain

The somatosensory system is made up of three separate and interacting systems.

• Exteroceptive: external stimuli

• Proprioceptive: body position

• Interoceptive: body conditions (e.g., temperature and blood pressure)

Cutaneous Receptors

• Free Nerve Ending

  • Temperature and pain

• Pacinian Corpuscles

  • Adapt rapidly; large and deep; onion-like

  • Respond to sudden displacements of the skin

• Merkel’s disks: gradual skin indentation

• Ruffini endings: gradual skin stretch

• Dermatome: the area of the body innervated by \n the left and right dorsal roots of a given segment of spinal cord

Two Major Somatosensory \n Pathways

Dorsal-Column Medial-Lemniscus System

• Mainly touch and proprioception

• First synapse in the dorsal column nuclei of the \n medulla

Anterolateral System

• Mainly pain and temperature

• Synapse upon entering the spinal cord

• Three tracts: spinothalamic, spinoreticular, \n spinotectal

Cortical Areas of \n Somatosensation

• Primary Somatosensory Cortex (SI)

  • Postcentral gyrus

  • Somatotopic organization (somatosensoryhomunculus); more sensitive, more cortex

  • Input largely contralateral

• SII: mainly input from SI

  • Somatotopic; input from both sides of the body

• Much of the output from SI and SII goes to \n the association cortex in the posterior \n parietal lobe.

Effects of Damage to the \\n Primary Somatosensory Cortex

Effects of damage to the primary somatosensory cortex are often mild.

* Likely due to numerous parallel pathways

Somatosensory System and \n Association Cortex

The highest level of the sensory hierarchy is made up of areas of association cortex in the prefrontal and posterior parietal cortex.

• The posterior parietal cortex contains bimodal neurons.

• Neurons that respond to activation of two different sensory systems

• Allow integration of visual and somatosensory \n input

Somatosensory Agnosias

• Astereognosia: inability to recognize objects by touch

  • Pure cases are rare; other sensory deficits areusually present.

• Asomatognosia: the failure to recognize parts of one’s own body (e.g., the case of the man who fell out of bed)

Perception of Pain

Despite its unpleasantness, pain is adaptive and needed.

• There exist no obvious cortical representation of pain (although the anterior cingulate gyrus appears to be \n involved in the emotional component of pain).

• Descending pain control: pain can be suppressed by cognitive and emotional factors.

Descending Pain Control

Circuitry Identified by the Following Studies:

• Electrical stimulation of the periaqueductal gray (PAG) has analgesic effects.

• PAG and other brain areas have opiate receptors.

• Existence of Endogenous Opiates (Natural \n Analgesics); Endorphins

Neuropathic Pain

• Neuropathic pain is severe chronic pain in the absence of a recognizable pain stimulus.

• Neuropathic pain is likely the result of pathology of the nervous system linked to an injury.

• Some evidence exists to suggest that aberrant microglial cell signals trigger neural pain pathways

Chemical Senses: Smell and Taste

Olfaction (Smell)

• Detects airborne chemicals

• Gustation (Taste)

  • Responds to chemicals in the mouth

• Food acts on both systems to produce flavor

• Pheremones are chemicals that influence that \n behavior of conspecifics (members of the same \n species).

• Evidence of Human Pheromones

• Changes in Olfactory Sensitivity across the \n Menstrual Cycle

• Synchronization of Menstrual Cycles

• Sex Identification by Smell (Especially by Women)

• Men can identify a woman’s menstrual stage by smell

Olfactory System

• Receptor cells are embedded in the olfactory mucosa of the nose.

• There are many different kinds of receptors.

  • Rats and mice have about 1,500.

  • Humans have almost 1,000.

• Same kinds of receptor cells project to similar areas \n of the olfactory bulb.

• Clusters of neurons near the surface of the olfactory bulbs

  • Olfactory glomeruli

• New receptor cells are created throughout life.

• The olfactory tract projects to several structures of the medial temporal lobes including the amygdala and the piriform cortex.

  • Does NOT first pass through the thalamus

  • Only sensory system that does this

Gustatory System

• There are receptors in the tongue and oral cavity in clusters of about 50 called taste buds.

  • Located around small protuberances called papillae

• There are 4 (sweet, sour, salty, bitter) primary \n tastes; 5th is umami, meat or savory.

• Many tastes are not created by combining \n primaries.

• Salty and sour don’t have receptors; they \n merely act on ion channels

• Gustatory afferent neurons leave the mouth as part of the 7th, 9th, and 10th cranial nerves to the solitary nucleus of the medulla.

• Projections then pass to the ventral posterior nucleus of the thalamus.

• From there, neurons project to the primary gustatory cortex and then to the secondary gustatory cortex

Brain Damage and the \n Chemical Senses

Anosmia: inability to smell

• The most common cause is a blow to the head \n that damages olfactory nerves.

• Incomplete deficits are seen with a variety of \n disorders.

Ageusia: inability to taste

• Rare due to multiple pathways carrying taste \n information

• There is evidence for the narrow tuning of \n gustatory receptors.

• Respond to only one taste

• Tuning is broader in presynaptic cells and up through the cortex

Selective Attention

• Selective attention improves perception of what is attended to and interferes with that which is not.

• Internal cognitive processes (endogenous attention) and external events (exogenous attention) focus attention

• The cocktail party phenomenon indicates that there is processing of information not attended to

Change Blindness

Change blindness: no memory of that which is not attended to

* We do not appear to remember parts of a scene that are not the focus of our attention.

Neural Mechanisms of Attention

• Selective attention is thought to work by strengthening the neural responses to attended-to aspects and by weakening the responses to other.

• For example, spatial attention can shift the location of receptive fields (Wommelsdorf et al., 2006)

Simultanagnosia

Simultanagnosia: a difficulty in attending to more than one visual object at a time

* Typical cause: bilateral damage to the dorsal stream (involved with localizing objects in space)

The primary sensory cortex of a system is the area of sensory cortex that receives most of its input directly from the _______ relay nuclei of that system.

 Thalamic

Sensation and perception are _____.

 two phases of the general process of perceiving

In _____systems, information flows through and is conducted over _____ pathway(s), whereas in _____systems, information flows through and is conducted over _____ pathway(s).

serial; one; parallel; multiple

How does the brain combine individual sensory attributes to produce integrated perceptions? This is called the ______________.

binding problem

The function of the _________ system is the perception of sound.

auditory

In the conduction of sound, the vibration of the _____ triggers vibrations of the _____ which transfers the vibrations to the fluid of the cochlea.

 stapes; oval window

Which structures within the ear dissipate the vibrations that occur in cochlear fluid?

 Round window

The organization of the auditory system is primarily _____

tonotopic

The _____ functions to locate sources of sensory input in space.

superior colliculi

The frequency of sound is converted into the perception of pitch in the _____ cortex.

small area anterior to the primary auditory

Conductive deafness results from damage to the _____, whereas nerve deafness results from damage to the _____

ossicles; cochlea or auditory nerve

A blind person frequently identifies objects by touching them. This is known as _____.

stereognosis

Information about pain and temperature that occurs within the face is carried by the _____ nerve.

 trigeminal

The _____ is located in the area of the postcentral gyrus, just ventral to SI.

secondary somatosensory cortex

The primary somatosensory cortex possesses _____ functional strips, each with a similar, but separate ________ organization.

four; somatotopical

_____ is a common component of contralateral neglect resulting from a _____ hemisphere injury.

Asomatognosia; right

Hemispherectomized patients can perceive pain as emanating from _____ of the body.

both sides