Simon Flashcards
<p>What is properties of colour</p>
<p>- Interpretation of the brain</p>
<p>- Context-specific</p>
<p>What did Issac Newton found in colour</p>
<p>White light is made up up of all visible</p>
<p>What did Young and Helmholtz found in colour</p>
<p>3 receptors - Trichromacy RGB</p>
<p>What did Edwalrd Hering sugest</p>
<p>Opponency: Red-Green; Blue-Yellow.</p>
<p>First stage: trichromatic</p>
<p>Second stage: Opponent stage</p>
<p>Define neural substrate</p>
<p>Indicate a part of the nervous system underlying a behaviour or physiological state</p>
<p>Kraukskopf (1982): Aims</p>
<p>Aims: Simple colour detection (Presence or Absense binary)</p>
<p>Kraukskopf (1982): Method</p>
<p>- Small disc whose colour varied in time along an axis of opponent colour space</p>
<p>- Participants indicated test pulse visiblitybefore/after prolonged exposure to a stimulus modulated along given axis</p>
<p>- Contrast/visibility of pulse varied until "threshold" reached (75% correct)</p>
<p>What is a colour space</p>
<p>Method by which a light and colour may be represented such that its definition is unique and replicable </p>
<p>What are the 3 cones.</p>
<p>L Cones: Reds</p>
<p>M Cones: Green</p>
<p>S Cones:: Blue</p>
<p>What is the cardinal colour space</p>
<p>2 Chromatic Axes (Colour): R-G; B-Y</p>
<p>1 Achromatic Axis: Luminance</p>
<p>What is the cone's relationship to the cardinal colour space (What does S,M,L correspond to). Which one is luminance</p>
<p>Bluish Yellowishness: S - (L+M)</p>
<p>Reddish Greenishness: L-M</p>
<p>Blackish Whitishness: L+ M</p>
<p>Kraukskopf (1982): Outcome measure</p>
<p>Distance from centre = Adapted - Unadapted Threshold</p>
<p>(Bigger difference from centre = More adaptation effect)</p>
<ul> <li>If adapted someone on R-G and tested on B-Y <ul> <li>Distance from centre = 0</li> </ul> </li> <li>If adapted someone on R-G with greatereffects on tulse pulse on R-G, distance from centre <ul> <li>Distance from centre + big</li> </ul> </li></ul>
<p>Kraukskopf (1982): Results Interpretation</p>
<p>2 Chromatic and 1 Acrhomatic Axis = Opponency</p>
<p>1.) Each axis shows independent adaptability/orthogonality</p>
<ul> <li>Threshold only raised by adapting to a stimulus along the same axis (unaffected by adaptation to other axes)</li> <li>3 independent detection mechanisms mediate the transmission of spatio-chromatic information from retina to cortex</li></ul>
<p>In psychophysics, who are the subjects</p>
<p>Neurons. </p>
<p>What are cardinal neurons. Are there any?</p>
<p>Group of neurons involved in colour vision</p>
<p>No. No single "cardinal neuron"</p>
<p>What are properties of cardinal neurons (if any)</p>
<p>1.) Chromatic sensitivity clustered along cardinal axes (RG/BY): To get pattern of independent adaptability</p>
<p>2.) Adapatation/ Change in output after prolonged exposure</p>
<p>How does the visual system work</p>
<p>Photoreceptors > Horizontal > Bipolar > Retinal Ganglion Cell (Difference in sensitivity) > LGN > Cortex</p>
<p>LGN and Cortex connections</p>
<p>More V1 to LGN<br></br>LessLGN to V1</p>
<p>What are cells in the layers of the LGN</p>
<p>1.) Parvo Cellulular (P Cells) : Small</p>
<p>2.) Konio Cellulular: Medium</p>
<p>3.) Magno Cellular (M Cells): Big</p>
<p>Derrington (1984): Aim</p>
<p>Are the 3 LGN cells grouped along in cardinal axis? </p>
<p>Derrington (1984): Stimuli and Methods</p>
<p><u>Macaque LGN neuron</u></p>
<ul> <li>Coloured spot stimuli to establish receptive field <ul> <li>Examine neuronal output changes as a function of colour and luminance properties</li> <li>Modulated across 3 orthognal planes until"null response" is found</li> </ul> </li> <li>Silent substitution method</li> <li>Preferred stimulus of neuron = Orthogonal to null plane in 3D space</li></ul>
<p>What is the silent substitution method in Derington (1984)</p>
<p>Two coloured light exchange with no effect on output of neurons</p>
<p>This indicates that the neurons are inresponsive and the preferred stimulus is orthogonal (right-angle)</p>
<p>Derrington (1984): Results</p>
<p>Neurons "chromatic signature" fell into 3 subgroups.</p>
<p></p>
<p></p>
<p>Derrington (1984): Results from P Cells</p>
<p>1.) Parvo Cellular</p>
<p>Less sensitive to luminance</p>
<p>Senstivity to colour (RG or BY)</p>
<p></p>
<p>Derrington (1984): Results from K cells</p>
<p>2.) Konio Cellulular: Not sure. But they have a large number of S cones (maybe augment)</p>
<p>Derrington (1984): Results from MCells</p>
<p>3.) Magno Cellular:</p>
<p>Very sensitive to luminance</p>
<p>NO colour sensitivity.</p>
<p>Can Derington's (1984) study concludecardinal properties of neurons?</p>
<p>Not fully.</p>
<p>Remember they need to fulfil 2 properties: (1) Chromatic Senstiivity (2) Adaptation</p>
<p>They onlyestablished chromatic signature, not adapatation</p>
<p>Krauskopf (1990) Aim</p>
<p>Replicate Derington (1984) in the cortex</p>
<p>Krauskopf (1990) Results</p>
<p><u><strong>V1</strong></u></p>
<p>- In each cortical group, lack of clustering (i.e. neurons redistributed across colour plane) suggestno cardinal signature</p>
<p>- Showed strong adaptation effect (Reduce output after prolonged exposure)</p>
<p>LGN vs V1 neurons</p>
<p>LGN: Cardinal colour signature but no adaptation</p>
<p>V1: No cardinal colour signature but adapt</p>
<p>What does all the findings suggest in about cardinal behaviour? Which neurons?</p>
<p>LGN (Chromatic Signature) + V1 (Adaptation) = Detection of presence.</p>
<p><u><strong>Cardinal Behaviour</strong></u></p>
<p>There is no modulation of colour. There is no "cardinal neurons" doing "cardinal behaviour". Can only be explained on the basis of a combination of LGN and cortical properties</p>
<p>Does detecting modulations in colour rely in output of local/distributed neurons</p>
<p>Distribution representation, notoutput of local/individual neurons</p>
<p>What are the 2 evidences to suggest that detecting colour modulation is part of a distributed representation</p>
<p>1.) Psychophysical sensitivity to chromatic stimuli far better than that of any individual neuron</p>
<p>2.) Different neural expansions in Magnocellular and Parvocellular pathways from retina to V1</p>
<p>First evidence that colour modulation is part of a distributed network:</p>
<p>Psychophysical sensitivity to chromatic stimuli > neuronal senstivity. What does sensitivity mean and how does it relate to threshold?</p>
<p>More sensitive = Lower threshold level needed to identify stimulus.</p>
<p>We need lower threshold to identify colour than luminance</p>
<p>Colour vs Motion: Neuronal Properties, Which Cells in the LGN, Feedback</p>
<p>Colour</p>
<ul> <li>Population Neurons</li> <li>P cells</li> <li>Feedback between V1 and LGN <ul> <li>Feedback takes time</li> <li>Hence, we are not very good at looking at colours move</li> </ul> </li></ul>
<p>Motion:</p>
<ul> <li>Potentially single neurons</li> <li>M cells (Luminance)</li> <li>Little feedback between V1 and LGN <ul> <li>Feedback takes time</li> <li>Hence, we are good at detecting luminance motion.</li> </ul> </li></ul>