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 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 Attention

Pestillli & Carrasco, Vis.Res. 2005

Pestilli & Carrasco, Vis.Res. 2005

Pestilli & Carrasco, JoV 07

adaptation

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

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

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

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

Contrast appearance n=16 Contrast of Test stimulus % perceived contrast test > Standard Test cue Neutral cue Standard cue p.s.e.

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

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

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

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

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 Why use noise?

Campbell & Robson (1968)

Pelli & Farell 1999

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. 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. Lu & Dosher, 1998, 200, 2002, 2004

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

Signature of attention mechanisms

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

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

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

PTM Dosher & Lu. 2000