TESS MATTSON, CAITLIN SKLUZACEK, BLAINE FEIA, PENG JIAO 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 didnt 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 frequency Striate 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 side Stripe 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 cells 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.

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Further Complications End stopping These cells appear to be subclasses of the simple and complex cells Recent Research The size of a cells 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

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