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Introduction definition of the construct a bit of history Spatial attention and early vision

Attention. Introduction definition of the construct a bit of history Spatial attention and early vision contrast spatial resolution some experimental methods Feature based attention Visual search. Attention. Introduction a bit of history some experimental methods

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Introduction definition of the construct a bit of history Spatial attention and early vision

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  1. Attention • Introduction • definition of the construct • a bit of history • Spatial attention and early vision • contrast • spatial resolution • some experimental methods • Feature based attention • Visual search

  2. Attention • Introduction • a bit of history • some experimental methods • definition of the construct • spatial vs. feature-based vs. object-based • spatial: overt vs. covert attention • covert: endogenous (sustained) vs. exogenous (transient) • Spatial attention and early vision • contrast sensitivity • endogenous : contrast gain • exogenous: response gain • endogenous attention potentiates effects of adaptation • Contrast sensitivity • Exogenous: cost at unattended location • Exogenous overcomes adaptation and restores sensitivity • Attention signatures: Attention-plus-external noise paradigm

  3. Pestillli & Carrasco, Vis.Res. 2005

  4. Pestilli & Carrasco, Vis.Res. 2005

  5. Pestilli & Carrasco, JoV 07

  6. adaptation

  7. Transient attention and adaptation Attention: response gain ~ Ling & Carrasco, Vis. Res. 06 Adaptation: contrast gain Benefit and cost are similar regardless of adaptation state Attention overcomes adaptation and restores contrast sensitivity Pestilli & Carrasco, JoV 07

  8. Does attention intensify the sensory impression? YES.Wundt, Mach, Helmholtz & Titchener W. James Yes, but it does not ever lead us astray NO. Fechner

  9. . fixation point 500 ms neutral cue peripheral cue . cue 67 ms . ISI 53 ms . stimuli 40 ms . response 1 s “what is the orientation of the higher contrast stimulus?” Methods - non-predictive peripheral cue - 2 x 2 AFC task: orientation contingent on apparent contrast

  10. Stimuli Standard: 6 or 22 % contrast Test: 2-80 % contrast

  11. Contrast appearance 100 n=16 p.s.e. 50 % perceived contrast test > Standard Test cue Neutral cue Standard cue 0 1 10 100 Contrast of Test stimulus

  12. Contrast appearance SOA - 500 ms SOA - 100 ms 100 % perceived contrast: Test > Standard 50 Test cued Neutral cue Standard cued n = 16 n = 16 0 1 10 100 1 10 100 Contrast of test stimulus Other controls: inverted instructions, postcue, cue polarity, appearance judgment w/o concurrent task

  13. 16% 22% 28% Attention alters contrast appearance Neutral Standard Cued Test Cued Carrasco, Ling & Read Nature Neurosci, 2004

  14. Attention & appearance • spatial frequency Goebell & Carrasco, 2005 • apparent size Anton-Erxleben & Treue, 2007 • motion coherence Liu, Fuller & Carrasco, 2006 • flicker Montagna & Carrasco, 2006 • speed Turatto et al., 2007 • saturation, not hue Fuller & Carrasco, 2006

  15. Covert attention • enhanced contrast sensitivity at attended location; diminished sensitivity at unattended location • transient: • performance – response gain • appearance • restores effects of adaptation (contrast gain) • sustained: • performance – contrast gain • strengthens adaptation

  16. Why use noise? Noise limits all forms of communication, including vision. Visual sensitivity is a product of two factors that are each invariant with respect to many properties of the stimulus and task. By estimating efficiency and equivalent noise, one can isolate visual processes more easily than by using sensitivity measures alone. Measure the human observer's threshold with and without a noise background added to the display, to disentangle the observer's ability from the observer's intrinsic noise. Calculate ideal performance of the task at hand, as a benchmark for human performance. This strips away the intrinsic difficulty of the task to reveal a pure measure of human ability. Denis Pelli

  17. Campbell & Robson (1968)

  18. Pelli & Farell 1999

  19. Pelli & Farell 1999

  20. Perceptual template model (PTM) Theoretical and empirical framework to assess the mechanisms of attention by systematically manipulating the amount and/or characteristics of the external noise added to the stimuli and measuring modulation of perceptual discriminability. Perceptual processes are limited by various sources of noise - intrinsic stimulus variability, receptor sampling errors, randomness of neural responses, loss of information during neural transmission. Lu & Dosher, 1998, 200, 2002, 2004

  21. External noise distinguishes mechanisms of attention samples of 8 levels of external noise a Gabor embedded in the external noises TVC functions, 3 d’

  22. Signature of attention mechanisms

  23. 150 ms precue valid : invalid (5:1) 675 ms response cue noise signal 17 ms Attention-plus-external noise paradigm 4 possible orientations 8 external noise levels method of constant stimuli

  24. External noise exclusion (but Ling & Carrasco ’06) External noise exclusion & stimulus enhancement

  25. Signal enhancement suprathreshold target stimulus no distracters no local or global masks no location uncertainty response cue e.g.,Cameron, Tai & Carrasco 2002; Ling & Carrasco, 2006

  26. PTM Dosher & Lu. 2000

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