Transcript Other Receptive-Field Properties

Striate Receptive Fields
TESS MATTSON, CAITLIN SKLUZACEK,
BLAINE FEIA, PENG JIAO LI, LUCAS
MENDEN, JAMES LOONEN, CHAARISSA
ROMERO
David Hubel and Torsten Wiesel
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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)
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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
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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 frequency
 Striate cortex tuned to a particular frequency
 Function as a filter
 Respond to moving lines, bars, edges, and gratings
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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
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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 side
 Stripe detector
 Responds best by a line of light with a specific width with
darkness surrounding both sides
Complex Cell
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A neuron whose receptive-field characteristics cannot be easily
predicted by mapping with spots of light.
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A complex cell will respond regardless of where the stripe is
presented, as long as it is somewhere within the cell’s receptive
field
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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).
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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.
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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&f
eature=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
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Key Terms
 Orientation tuning- the tendency of neurons in striate cortex to
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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.ht
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