1. Attention and Perceptual Learning Modulate Contextual Influences on Visual Perception 
Minami Ito, Gerald Westheimer, Charles D Gilbert 
Neuron 
Volume 20, Issue 6, Pages (June 1998)
DOI: /S (00)

2. Figure 1 Experimental Design
(A) Stimuli and sequence of presentation with a standard “four position” stimulus. Lines were bright against a dark background. The subject fixated the central spot (fixation point) and had to judge whether the target line was brighter or dimmer than the reference. In the “focal attention” trials, the observer was cued on which of the four peripheral lines was the target line during that exposure; in the “distributed attention” trials, any of the four could be the target. The diagram illustrates the sequence of events for a trial. In each trial, several stimuli were presented after one cue presentation, and subjects reported on each stimulus. The number of repetitions was changed in random fashion; the figure describes two stimulus presentations.
(B) Appearance of the screen during stimulus presentation.
(Left) Basic pattern of fixation point, reference line, and four peripheral test lines, one of which would be the target. (Right) To examine the contextual effect, there was a set of somewhat brighter flanking lines in addition to a basic pattern.
(C) Mean and standard deviations in the horizontal and vertical meridians of eye positions during stimulus presentation in a primate subject (UM, left) and a human subject (MI, right). Position was measured during stimulus presentation time (100 ms) while subjects performed the brightness discrimination task. The means and standard deviations were calculated during a 1 day session for each horizontal and vertical direction and for each cued location. In each attentional condition, the mean eye position was calculated for each target location. Data points overlapped between focal attention (diamonds) and distributed attention (squares). The small circles in the four corners indicate the locations of test lines.
Neuron  , DOI: ( /S (00) )

3. Figure 2 Typical Results of Attentional Effects in One Human Subject
Two psychometric curves were obtained with each attentional state, one without (square) and the other with (circle) contextual flanks. Coordinates show the percent of “target line appears brighter than reference” responses as a function of luminance level of the target line expressed as a ratio of the luminance of the reference. The value 1 refers to luminance of the reference line. Continuous lines indicate the best-fitting psychometric curves obtained by the probit method, which yielded two measures: the threshold from the slope of the curves and the shift from the difference in brightness match to the reference. A shift of the psychometric curves toward the left indicates facilitation due to the flanking lines. Data demonstrate that the brightness discrimination is better (threshold is lower) and the contextual influence is less (shift is smaller) with focal attention than with distributed attention.
Neuron  , DOI: ( /S (00) )

4. Figure 3
Effect of Attention on Brightness Thresholds and Contextual Facilitation
Data for our seven subjects, including monkeys (SA and UM), for brightness discrimination (A and C) and contextual facilitation (B and D) from results such as those shown in Figure 2.
(A and B) Gray and black bars refer, respectively, to the distributed and focal attention regimens. Error bars and levels of significance (*p < 0.05, **p < 0.01) are shown above each set of paired conditions. Attentional modulation was consistent among our subjects.
(C and D) Averaged data for all seven observers. Brightness discrimination thresholds, both with and without contextual flanks, are better by a factor of about two when a previous cue instructs the observer of the expected position of the target than when all four possible target locations are equally likely. On the other hand, the flanks have a much higher influence on the target brightness when the attention is distributed.
Neuron  , DOI: ( /S (00) )

5. Figure 4 Influence of Training on Brightness Thresholds
Time course of the improvement of the threshold for a human subject (A) and a monkey (B). Threshold was measured weekly under distributed attention (square) and focal attention (circle) during the training period. Error bars show the standard error of the mean yielded by the probit method. (C) shows the threshold averaged among our seven subjects, including monkeys. The training reduced the brightness discrimination threshold by a factor of about two when all four possible target locations are equally likely. On the other hand, improvement was limited when a previous cue instructed the observer as to the expected position of the target.
Neuron  , DOI: ( /S (00) )

6. Figure 5 Influence of Training on Contextual Facilitation
(A) Amplitude of facilitation plotted in each weekly session under distributed attention (square) and focal attention (circle). Initially, facilitation is larger under distributed attention than focal attention. Training reduced facilitation under distributed attention, thereby eliminating the difference observed initially between distributed and focal attention.
(B) Results averaged for all seven observers. The training reduced the effect of facilitation by a factor of about three when the observer had to distribute his attention to all four possible target locations.
Neuron  , DOI: ( /S (00) )

7. Figure 6 Transfer of Training Effects to Untrained Locations
The threshold of the brightness discrimination was measured with the “untrained positions” stimulus only on the second and last weeks of the training period. The untrained stimulus was given by rotating the original “four position” stimulus by 45°. The averaged result from three human subjects (KI, PN, and AG) showed similar reduction of the threshold in the “untrained positions” as in the trained positions.
Neuron  , DOI: ( /S (00) )