Sensation and Perception Flashcards
What is sensation and perception?
- sensation is the detection of simple properties e. brightness, colour, loudness, sweetness
- perception is the interpretation of sensory properties e.g object recognition, identification of properties such as size, location etc
What do sensory systems need?
- a biological mechanism for translating physical attributes into electrical signals (receptors)
- mechanism for conveying this information to CNS
What are receptors?
- Most sensory detectors are modified neurons
- neurons transmit brief electrical pulses with fixed amplitude and duration
- they make connections with each other to create networks with one-to-many or many-to-one linkages
How do receptors work with vision?
- Receptors in the retina of the eye are rods and cones
- they are modified neurons containing photosensitive pigment (rhodopsin)
- Rods function at low light levels, and cones function in bright light
Which receptor is used for perception of colour?
- Cones are colour-tuned so they have peak sensitivity to red, green and blue
- Cones are colour sensitive, so their output depends on wavelength of light
- For any wavelength, colour is uniquely coded by an output pattern
- White light is a mix of all wavelengths ( red green blue receptors)
What is the structure of a retina?
- Retina contains around 120 million rods and 7 million cones, all interconnected
- The optic nerve is formed from axons of 1 millions ganglion cells
- The structure of the retina is built through a network of connections between receptors and optic nerve
What computations does the retina perform?
- the response of photoreceptors and bipolar cells to illumination is graded
- amacrine cells and horizontal cells combine and contrast signals from adjacent photoreceptors
- ganglion cells generate potentials and form the optic nerve
What is a single-cell recording?
Electro-physiological response of a single neuron can be observed by inserting a micro electrode
What is feature detection?
- Electrical responses monitored in a single cell when bright lights in different orientations are projected onto a small area of the retina
- particular cells are selectively active in response to a particular stimulus in a particular orientation (feature detectors)
What is segmentation of the visual scene? (perception)
- It is the first stage of object recognition, so visual features that belong to the same object are grouped together
- A prerequisite for object recognition is figure-ground perception (the visual ability to differentiate an object(figure) from its background(ground) )
What is Gestalt principles of grouping?
- The grouping of elements to make a figure is determined by a set of basic principles that are automatic and innate (evidence from studies of infants)
What is the ‘visual cliff’ ?
- An apparatus made to test whether animals/infants are able to interpret depth cues, to see whether depth perception is innate
- studies showed that out of 36 babies, 27 were willing to move onto shallow side whilst only 3 to deep side
Summary of sensation
- It involves the conversion of physical energy into signals in sensory neurons (receptors)
- It requires specialised sense organs, containing receptors which convert the physical energy into neural signals
Perception summary
-Perceptual processing is based on interpretation, so perceptual mechanics are designed to provide awareness of physical reality, rather than appearance
- Observers do not have direct access to sensory data
- Interpretation is bases on both innate principles of perceptual organisation, and stored knowledge about the world
