Chapter 7 Sensory Systems, Perception, and Attention

Three sensory areas of the cortex

Three sensory areas of the cortex

Primary, Secondary, Association

Primary Sensory Cortex

-Receives most of its input from thalamic relay nuclei related to specific sensory system

Secondary Sensory Cortex

These areas receive input from the primary sensory cortex or from other secondary areas within the same system

Association Cortex

This region integrates information from multiple sensory systems, with most input coming from the secondary sensory cortex.

Hierarchial Organization

Based on specificity & complexity of function. Flow through brain structures in order of increasing complexity (early areas process simple stimuli, later areas process more complex stimuli).​

Functional Segregation

Each of the three levels of the cerebral cortex (primary, secondary, and association) is organized so that different parts of the various structures specialize in different kinds of analysis.​

Parallel Processing

Sensory systems are organized so that information flows between different structures simultaneously along multiple pathways.​

Former Model vs Current Model

-Old model is hierarchical, functionally homogeneous, and serial

-Current model is hierarchical, functionally segregated, and parallel

Amplitude, Frequency, and Complexity are to

Loudness, pitch, and timbre

Fourier Analysis

Takes complex sound waves and simplifies it into simple sine waves

Pathway of Sound

-Sound waves → auditory canal →tympanic membrane (eardrum) vibrates.​

-Vibrations of the stapes stimulate the oval window membrane vibrations spread to the fluid of the cochlea, a snail-shaped structure that contains the organ of Corti (the auditory receptor organ, includes basilar membrane and the tectorial membrane).​

-Pressure changes at the oval window create waves along the organ of Corti.​

-Auditory receptors (hair cells) are situated in the basilar membrane, the tectorial membrane rests on these hair cells.​

-Deflection of the organ of Corti exerts shearing force stimulating hair cells.​

-This stimulation increases firing in the axons of the auditory nerve.​

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Structures involved in auditory transduction

-Auditory canal

-Tympanic membrane

-Ossicles (malleus, incus, and stapes)

-Oval window

-Cochlea

-Organ of corti (basilar membrane and tectorial membrane)

-Auditory Receptors (hair cells)

The cochlea is organized tonotopically

-Meaning that different regions respond to different frequencies.​

Higher frequencies vs lower frequencies

-HF: activate hair cells closer to the cochlear window

-LF: activate hair cells near the tip

The Challenges of Audition

The auditory system manages to categorize and combine these frequency messages, allowing us to hear each sound source independently.​

Pathway from Ear to Primary Auditory Cortex​

• Auditory nerve axons synapse in the ipsilateral cochlear nuclei.​

• Projections from the cochlear nuclei lead to the superior olives.​

• Olivary neurons project via the lateral lemniscus to the inferior colliculi.​

• Neurons in the inferior colliculi synapse on those projecting to the medial geniculate nuclei of the thalamus.​

• Finally, the medial geniculate nuclei project to the primary auditory cortex.

Primary Auditory Cortex

-In the temporal lobe, concealed within the lateral fissure, mainly receiving inputs from the medial geniculate nucleus.​

-Three regions: core, belt, parabelt

Organization of Primary Auditory Cortex:

-Similar to the primary visual cortex, the primary auditory cortex is organized in functional columns. ​

-Neurons in the same column respond best to sounds within the same frequency range.​

-Tonotopic Layout

-Recognize temporal components of sound, particularly variations in the amplitude of sound frequencies over time. ​

Study of Primary Auditory Cortex

-Neurons in the auditory cortex often respond weakly to simple stimuli like pure tones, traditionally used in studies.​

-Recent shifts in research practices include using natural sounds, which generally elicit stronger responses from neurons in the mammalian auditory cortex.

Analysis of Primary Auditory Cortex

Auditory cortex integrates information about current perceptions and behaviors to produce relevant auditory signals.

Auditory Objects

• For instance, it can distinguish and identify complex frequency mixtures, like those from a piano, and enable recognition of the sound as a piano.​

Dual Streams

• Anterior auditory pathway for identifying sounds (“what” pathway)​

• Posterior auditory pathway for locating sounds (“where” pathway)​

Auditory-Visual Interactions

• In studies, some posterior parietal neurons in monkeys have visual, auditory, or both types of receptive fields.​

• Functional Brain Imaging has shown sensory interactions not only in association cortex but also in primary sensory cortex.​

Auditory Cortex Damage

• Bilateral PAC lesions do not cause deafness​

• Hearing usually recovers​

• Difficulties processing structural aspects of sound (word deafness) remain.​

Two Types of Deafness

• Conductive (damage to ossicles)​

• Nerve (damage to cochlea or nerve →loss of hair cells)​

Age-related hearing loss

• Affects high frequencies ​

• Can cause problems discriminating between different sounds.​

• Risk or social isolation and cognitive decline​

• Helped by hearing aids or cochlear implant​

Cochlear Implant

• Bypass damaged auditory hair cells by converting sounds into electrical signals that stimulate the auditory nerve.​

• Offer significant benefits but don't restore normal hearing.​

• Timing of Implantation matters: The earlier the better.

Somatosensory System

-Processes sensations from the body (such as touch and pain)

Three Subsystems of somatosensory system

1. Exteroceptive cutaneous system (outside body)

2. Proprioceptive system (body position)​

3. Interoceptive system (within body)​

Exteroceptive Cutaneous System Breakdown

• Mechanical stimulation (touch)​

• Thermal stimulation (temperature)​

• Nociceptive stimuli (surface pain)​

Cutaneous Receptors

-Free nerve endings

-Paciniant Corpuscles

-Merkel Receptors & Ruffini Corpuscles

Free Nerve Endings

Pain and Temperature

Pacinian Corpuscles

Deep fast-adapting touch receptors

Merkel Receptors & Ruffini Corpuscles

slow-adapting touch receptors; skin stretching & indentations

Cutaneous Receptors

-All cutaneous receptors respond to stimuli with ion flow across membrane​

-Tactile sensations are not specific to individual receptors but are produced by multiple receptor mechanisms.​

Stereognosis

(identification of objects by touch) use both fast and slow-adapting receptors.

Two Major Somatosensory Pathways

1. The Dorsal-Column Medial-Lemniscus System for touch and proprioception.​

2. Anterolateral system for pain and temperature.​

Primary Somatosensory Cortex

• Organized somatotopically (according to a map of the body surface).​

• Larger areas body parts used for tactile discrimination (like hands, lips, tongue),​

Functional Strips

• Four functional strips, each with a separate somatotopic organization and sensitivity to different types of somatosensory input (touch or pressure).​

Bimodal Neurons

Neurons that respond to activation of two different system systems

Astereognosia

• Loss of ability to recognize objects by touch

Asomatognosia

• Loss of ability to recognize part’s of one’s own body​

• Damage to right temporal & posterior parietal cortex

Anosognosia

-Failure of patient to recognize their own symptoms.

Contralateral Neglect

-loss of awareness to one side of visual space.​

Rubber-Hand Illusion

• Hide healthy volunteer’s hand while stroking both the hidden hand and rubber hand​

• The rubber hand is placed in clear sight​

• Volunteers quickly perceive rubber hand as their own​

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Pain Perception

• Pain, despite being an unpleasant experience, is crucial for survival.​

• It serves as a warning against potentially harmful activities and prompts seeking treatment.​

Pain activates what cortices

-It activates multiple cortical areas including the thalamus, SI and SII, the insula, and the anterior cingulate cortex (emotional component of pain)

-MOST COMMONLY ASSOCIATED IS ANTERIOR CINGULATE CORTEX

Cognitive and Emotional Modulation of Pain

• Pain perception can be significantly influenced by cognitive and emotional factors. ​

• Reduced pain during intense religious ceremonies, soldiers experiencing less pain during battle, or people not feeling pain in life-threatening situations until the danger has passed.

Gate-Control Theory

Melzack and Wall (1965) were impressed by the ability of emotional and cognitive factors to block pain; they concluded that there must be a circuit descending from the forebrain that can block incoming pain signals

Periaqueductal Gray (PAG)

-receptors for opiate analgesics (e.g., morphine) in the PAG and several other sites; this suggested that the body produced its own opiates (called endogenous opiates or endorphins), and several were subsequently isolated.​

-has pain blocking effects

Neuropathic Pain

• severe chronic pain without a clear stimulus which often persists after an injury has healed and can be triggered by mild stimuli.​

Prior Knowledge has a major influence…

On how we perceive the world

Perceptual Decision Making

• Researchers suggest that we form mental models of the world through predictable and recurring sensory events. Our brains are viewed as "prediction machines" that actively construct models of ourselves and the world using our five senses.​

• The brain continuously makes decisions about what we should perceive, influenced by prior experiences, predictions and current sensory inputs.​

• Perceiving bistable figures, for example, seems like it should be a simple perceptual task, and yet clearly it is not.​

Bistable Figures

• figures, for example, seems like it should be a simple perceptual task, and yet clearly it is not.​

Binding Problem

• how the brain combines individual sensory attributes (shape, color, texture) to form integrated perceptions.​

Binding Problem and Solution

1. A single area atop the sensory hierarchy, possibly the claustrum, may integrate signals from all sensory systems.​

2. No single area is responsible; instead, integration results from interactions at each cortical level, including primary sensory cortices and exchanges of information between sensory cortices within and across modalities.​

3. Subcortical structures might also contribute to this sensory information exchange.​

Selective Attention

• Attention facilitates the selection and processing of some stimuli at the expense of others.​

Cocktail-party phenomenon

• Salient, unattended information can capture attention.​

• Demonstrates how the brain can concentrate on specific stimuli, blocking others from conscious awareness while still unconsciously monitoring them for potentially important or relevant information.​

Endogenous/ top-down

-Internal Cognitive Processes

-I control it

Exogenous/ bottom-up

-By external events

-Loud sound, grabs my attention

Change Blindness

• Two photographs identical in every aspect but one. If allowed a brief delay, people have difficulty seeing change​

• Explanation: no memories formed for unattended parts of a scene. ​

Attentional effects on the neural responses to stimuli

• Attention strengthens neural responses to attended stimuli and weakens responses to others.​

• Attention to locations increases activity in corresponding retinotopic areas.​