What are the 3 fundamental steps of information processing?
Which is the conscious process: perception or sensation?
What is transduction?
It's a multistep process where stimulus energy (electromagnetic, mechanical or chemical) is converted into electrical potentials that can be interpreted by the nervous system
What is a receptor potential?
What needs to happen for it to fire?
It's a graded response to a stimulus that can be depolarizing or hyperpolarizing, OR BOTH.
They have a threshold in stimulus amplitude that must be reached before they'll fire
What will happen to the receptor potentials when the stimuli is particularly intense?
Their amplitude will saturate
What is a receptive field, and how is it defined anatomically?
FOr each receptor cell there is a small aprt of the world it encodes for - it's the spatial region where a stimulus will produce a response
anatomically it's defined by the dendrites to the receptor cells
NOTE: receptive fields can overlap = redundancy
What makes up a sensory unit?
the primary afferent and any receptors that define its receptive field
How can a receptor encode stimulus modality?
By responding to one form of energy more than any other
individual receptors responsing only to a narrow range of that energy
The type of energy that a receptor responds to under normal conditions is called the ____, while an ____ is of a different typ eof energy that will cause the receptor to respond only if intense enough.
adequate stimulus (light for vision)
inadequate stimulus (pressure for vision)
What theory explains why an inadequate stimulus is perceived as the adequate stimulus?
THe labelled line theory
We learn and "map" sensations in a way that our brain will perceive pressure on the eye as light because that's the signal that is usually transmitted by that pathway
What are the 3 main type sof energy humans can detect?
electromagnetic: light and thermal
mechanical: sound, gravity, head movement, tough, pressure, blood pressure
chemical: tastants, odorants, physiological modulators like O2 concentration
How is stimulus intensity encoded - two ways...
1. frequency coding - firing rate of sensory neurons increases with increased intensity
2. population coding - nuber of primary afferents responding increases through recruitment with increased intensity
If threshold is the minimal intensity ot produce a response and saturation is the maximal response, what is the difference between threshold and saturation?
Describe recruitment in more detail...
THis goes back to the idea of receptive fields overlapping...
1 neuron at the center of the field responds "best" because it has the lowest threshold for the stimulus and it will respond first
the adjacent neurons within the receptive field will respond next - they have a higher threshold for the stimulus
the more intense the stimulus, the more neurons will be recruited and via population coding, the brain will register this increase in intensity
What is adaptation and what is the difference between tonic adaptation and phasic adaptation?
Adaptation is the process by which the response of a receptor to a CONSTANT stimulus DECLINES over time
slow adaptation = tonic
rapid adaptation = phasic
Do all of our senses undergo adaptation?
The vast majority do, but out sensation of gravity does not
What is acuity?
the ability to localize a stimulus
What are the two things that determine acuity?
receptive field size = smaller field size - greater acuity
Receptor density = more receptors - greater acuity
What is the inherent paradox between intensity coding and acuity?
How is it solved?
the higher the intensity, the more neurons are recruited, the harder it should be to localize (in theory)
We solve this thorugh lateral inhibition
Describe lateral inhibition
It's a process that occurs IN THE CNS
Recruitment occurs in the PNS
the central axon sends out collaterals by inhibitory interneurons
As the action potential travels up the axon, the adjacent neurons are shut off and the difference in the action potential betin generated by the central neuron compared to the adjacent neurons becomes more pronounced
this preserves the fact that the center of the stimulus is generating excitation
ultimatley this depends on second order neurons