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TESS MATTSON, CAITLIN SKLUZACEK, BLAINE FEIA, PENG J IAO LI , LUCAS
MENDEN, JAMES LOONEN, CHAARISSA ROMERO
Striate Receptive Fields
David Hubel and Torsten Wiesel
Wanted to extend the work done by Stephen Kuffler Used spots of light to try and map the striate cortex, which
didn’t work While trying to make the cells fire with spots, they found
that when inserting a glass slide into the ophthalmoscope, they found this made the cells fire
Realized the cells were responding to the shadow cast by the edge of the slide as it swept across the light path
Found that the cells in the striate cortex are elongated, not circular, and responded more vigorously to bars, lines, edges, and gratings
Orientation Selectivity
Hubel and Wiesel (1962) Uncovered a number of other important properties of the
receptive fields of neurons in striate cortex Individual neuron will not respond equivalently to just
any stripe in its receptive field Orientation tuning- tendency of neurons in striate
cortex to respond optimally to certain orientations and less to others. Ex.- Piano Keys
More cells are responsive to horizontal and vertical orientations than to obliques
How are receptive fields in the LGN transformed into the elongated receptive fields in striate cortex? Hubel and Wiesel
Suggested concentric LGN cells that feed into a cortical cell are all in a row
• Later studies have shown that the arrangement of LGN inputs is indeed crucial for establishing the orientation selectivity of striate cells
• However, other evidence suggests that neural interactions within the cortex also play an important role in the dynamics of orientation tuning.
Other Receptive-Field Properties
Respond not only to bars, lines, and edges Gratings (collections of lines)
The right spatial frequencyStriate cortex tuned to a particular frequency
Function as a filter Respond to moving lines, bars, edges, and gratings
Other Properties cont.
Cells influenced by input from both eyes Unlike in LGN
5-cycle/degree grating at 45 degrees Responds whether in left or right eye
Ocular dominance
Simple Cells
Cortical nuerons with clearly defined excitatory and inhibitory regions
Edge Detector Light on one side of receptive field and darkness on the
other sideStripe detector
Responds best by a line of light with a specific width with darkness surrounding both sides
Complex Cell
• A neuron whose receptive-field characteristics cannot be easily predicted by mapping with spots of light.
• A complex cell will respond regardless of where the stripe is presented, as long as it is somewhere within the cell’s receptive field
• When tested with a drifting grating, the complex cell gives a robust response, with little or none of the modulation shown by simple cells(e.g. retinal ganglion and LGN cells).
• Another way of stating this difference is to say: simple cells are “Phase-sensitive” Complex cells are “Phase-insensitive”
Complex
• The receptive field of complex cells represent a pooling of the response of several subunits. The subunits give the complex cell its spatial frequency and orientation tuning, but the complex pooling operation makes the complex cell insensitive to the precise position of the stimulus within its receptive field.
• Evidence shows that complex cells represent a separate parallel pathway:
Both simple cells and complex cells get direct input from LGN neurons.
Complex cells
• are orientation selective. • have spatially homogeneous receptive fields (no separate
ON/OFF subregions). • are nearly all binocular. • perform length summation.
Video
http://www.youtube.com/watch?v=L8kC3zU1pqM
http://www.youtube.com/watch?v=IOHayh06LJ4&feature=related
Further Complications
End stopping These cells appear to be subclasses of the simple
and complex cells Recent Research
The size of a cell’s receptor field appears to vary with target contrast
Neurons can be influenced by stimuli that fall outside the classic receptive field
Key Terms
Orientation tuning- the tendency of neurons in striate cortex to respond optimally to certain orientations and less to others
Filter- an acoustic, electrical, electronic, or optical device, instrument, computer program, or neuron that allows the passage of some frequencies or digital elements and blocks the passage of others
Ocular dominance- the property of the receptive fields of striate cortex neurons by which they demonstrate a preference, responding somewhat more rapidly when a stimulus is presented in one eye than when it is presented in the other
Simple cell- a cortical neuron with clearly defined excitatory and inhibitory regions
Complex cells- a neuron whose receptive-field characteristics cannot be easily predicted by mapping with spots of light
End stopping- the process by which a cell in the cortex first increases its firing rate as the bar length increases to fill up its receptive field, and then decreases its firing rate as the bar is lengthened further
http://sites.sinauer.com/wolfe3e/chap3/striaterfF.htm