(7) From signals to sensations Flashcards
What do the senses do?
The senses convey specific information about some source of physical energy Each sensory modality has a “labelled line”
What are Labelled lines?
the concept that each nerve input to the brain reports only a particular type of information
What does each sensory modality have?
- Each sensory modality has specialised receptors for transduction
- Very specific receptors that can transform information
What do sensory modalitys respond to?
- Each sensory modality responds to a range of stimuli
- Response to stimuli which are specific range, not just one
What does each sensory modality have a set of
Each sensory modality has a set of codes
What type of codes do sensory modalitys have?
- Intensity coding - Location coding - Coding for specific object (colours, shapes, pitch)
- Codes for different types of information
What are Sensory Receptor Organs?
act as filters of the environment: they detect and respond to some events and not others (skins, eyes, ears)
What is a Stimulus?
- event that affects the sensory organ
- Taking information from the external environment to the brain
What do animals have?
All animals have specialised body parts that are sensitive to some forms of energy
What do sensory systems do?
Very diverse, yet they all solve the same task: They convert environmental signals into neural activity that can influence the motor system of the animal
How do Psychophysics study sensory processing?
use behavioural testing to establish the sensitivity of a sensory system and the “rules” of its operation.
How does Electrophysiological recordings study sensory processing?
Electrophysiological recording from the single neurons or small groups of neurons along the sensory pathway to find out how the neural circuitry gives rise to the perceptual abilities.
How does imaging in humans study sensory process?
- Imaging in humans that are doing perceptual tasks to identify the brain areas responsible.
- Taking information to the brain from external environment helps interaction and survival
What must be estimated from the sensory signal
qualitative features, quantitative features, temporal features, spatial location of the stimulus
What qualitative features need to be considered when looking at sensory signals?
Qualitative features such as colour or odorant often referred to as modality- what is it? (touch vision, modality of signal)
What quantitative features need to be considered when looking at sensory signals?
Quantitative features such as magnitude often referred to as the intensity of a stimulus
What temporal features need to be considered when looking at sensory signals?
Temporal features such as duration or frequency of a signal
What spatial location of stimulus need to be considered when looking at sensory signals?
Spatial location of a stimulus - where is it?
What is a common strategy of sensory systems?
A common strategy of sensory systems is to have separate neural pathways specialized for estimating different types of stimulus features.
What do visual systems analyse?
Visual system analyses colour, shape and movement in different brain regions
What are the two main functions of each sensory system?
detection and discrimination
What is detection?
Detection: The detection of a signal. Weak signals can be detected without the animal being able to finely discriminate any of its features (whether the stimulus is present)
What is discrimination?
Discrimination: Discrimination of some aspects of a sensory input. This is often referred to as estimation (what type of stimulus it is)
What is a Adequate stimulus?
type of stimulus for which a given sensory organ is particularly adapted
What is Transducer function of receptors?
The process in which a stimulus energy is transduced into the electrical response, which triggers an AP
Where does sensory processing start?
- Sensory processing starts with receptor cells
- A give receptor cell is specialized to detect particular energies or chemicals
What happens when the sensory process is exposed to a stimulus?
Upon exposure to the stimulus, a receptor cell converts that energy into a change in electrical potentials across its membrane (generating action potential)
What does the structure of the receptor determine?
The structure of the receptor determines the form of energy to which it will respond
What is a receptor potential?
Receptor Potential step between the arrival of energy at receptor cell and the initiation of an action potential. It is usually an EPSP
Transduction of Mechanical Signals
-Excitatory events:
- mechanical stimulation deforms the corpuscle
- deformation of the corpuscle stretches the tip of the axon
- stretching the axon opens mechanically gated ion channels in the membrane, allowing sodium ions to enter
- when the receptor potential reaches the threshold amplitude, the axon produces an action potential
What are the sensory receptors 4 functions?
sensory transduction, amplification, transmission and integration?
What is Sensory transduction?
(they transduce [transform/translate] the energy of a stimulus into a change in membrane potential). Coding and transforming physical energy into action potential
What is Amplification?
(they strengthen the energy of the stimulus. The action potential conducted from the eye to the brain contains 100,000 times more energy than the few photons of light that stimulated the receptor).
What is Transmission?
(action potentials from receptors, or from neurons connected to receptors, reach the CNS). Transmitted to the brain (sensory pathway)
What is Integration?
(receptors contribute to the processing of a signal. For example many receptors show sensory adaptation. This term means that they respond less during continued stimulation. Of course some receptors “adapt” more quickly than others).
What are the 4 attributes of the stimulus?
- Modality (touch)
- Intensity (how big)
- Location (where about)
- Duration
What is modality?
- The most basic mechanism for identifying the nature of a sensory input is via labelled lines
- The connections of “pain” and “touch” fibres in the somatosensory system are entirely different - stimulation of either leads to the appropriate sensation, referring to the body sensation, particularly touch and pain sensation
What is the Somatosensory system?
receptor is a specialized peripheral element that is associated with the peripheral process of a sensory neuron
In auditory and visual systems what receptor cells are present?
Auditory and visual systems, a distinct type of receptor cell is present. In the auditory system, the receptor synapses directly on the ganglion cell, whereas in the visual system, an interneuron receives synapses from the photoreceptor and in turn synapses on the retinal ganglion cell.
Messages from different senses use the same type of energy
action potentionals
How does each sensory modality send their action potentials?
The brain recognise the different sensations as separate and distinct - each sensory modality sends its action potentials along separate nerve tracts
The estimated intensity of a stimulus is…
not a linear function of the actual intensity (either logarithmic or power law)
Increases of a weak intensity signals generate
- a larger perceived increase than increases of a strong signal
- The percept saturates
A single neuron can code for stimulus intensity by…
changing the frequency of action potential transmitted, cannot cover full range of stimulus intensity, Only a limited range if intensities can be coded in this way, can change fire rating
Multiple receptor cells acting in parallel manner provide…
broader range for coding the intensity: as the strength of the stimulus increases new neurons are recruited
Intensity can be represented by…
the number of activated cells
What is Range fractionation?
different receptors are specialist in particular segment (fractions) of an intensity scale
Receptive field of a sensory neuron consists of…
a region of space in which a stimulus will alter the neuron firing rate.
Each sensory modality has…
its own receptive field
The receptor of each primary neuron can…
pick up information from a specific area (receptive field).
Receptive fields can be irregular in…
shape and overlap with receptive fields of other neurons
Each receptor has their own…
- Each receptor has their own receptive field
- Skin is full of receptive fields
Each sensory receptor activates…
pathways that convey unique positional information
Smaller receptive fields are…
greater acuity
Lateral Inhabitation is…
- Receptors are strongly activated
- Surrounding area is inhibited
When stimulation is maintained, receptors show…
Many receptors show progressive loss of response
What are Tonic receptors?
produce constant rate of firing as long as the stimulus is applied, pain, a receptor which the frequency of action potentials declines slowly or not all stimulation is maintained
What are Phasic receptors?
burst of activity but quickly reduce firing rate (adapt) if stimulus is maintained, sensory adaptation, the frequency of action potentials drop rapidly as stimulation is maintained
Sensory information reaches the thalamus…
which send the signals to the cortex
Primary sensory cortex swaps information with…
non-primary sensory cortex
Sensory information enters the CNS through the…
brainstem or the spinal cord
One sensory system influences the perception derived from…
another sensory system
Association areas (Multisensory areas) that do not represent exclusively a single modality bot show a…
mixture of inputs from different sensory modalities
Signals of two sensory modalities converge on a…
bimodal neuron
Synaesthesia results from…
“crossed wiring” in the brain
Some researchers believe that these crossed connections are…
present in everyone at birth, and only later are the connections refined
