The bias introduced by asking subjects to respond sooner in the speed condition should result in them basing their detection/discrimination decision on lower motion coherence levels, but it should not introduce bias in a choice for the direction of motion coherence.
The pLPFC activity is unlikely to encode absolute motion coherence levels, as the difference in coherence activity between the accuracy and speed conditions was not even discernable in the brain region (i.e., MT+) most sensitive to the type of motion coherence display used in the present experiment.
Long-term deprivation of normal visual inputs can cause perceptual impairments at various levels of visual function, from basic visual acuity deficits, through mid-level deficits such as contour integration and motion coherence, to high-level face and object agnosia.
Visual stimuli were dynamic dot patterns of low motion coherence, presented at three levels of coherence tailored to each subject (see Stimulus Levels, below).
To quantify responses to visual motion, activation (averaged across coherence levels) relative to baseline fixation was measured for patients and controls.
Each equivalent noise and motion coherence task consisted of three levels: a combined demonstration and criterion phase ('level 1'), a practice phase ('level 2'), and a threshold estimation phase ('level 3'level
Our results suggest that motion coherence thresholds reach adult-like levels by approximately 9 years, which is slightly earlier than previous accounts that have suggested that maturity is reached by 10 11 years of age (Gunn et al., 2002), or 12 14 years of age (Hadad et al., 2011).
To rule out this possibility, we analyzed the data from the calibration procedure (i.e., the initial stage of the experiment in which we determined the level of motion coherence for each subject).
In addition, subjects were told that a trial may or may not contain motion coherence, and that in those that contained motion coherence, this coherence level could begin to increase at any time during the trial.
In the motion coherence task, a single QUEST staircase of 75 trials tracked the minimum coherence level required for accurate (84% correct) direction discrimination.
We also included trials without motion coherence, as these trials assessed how the speed-accuracy instructions influenced baseline levels of activity in the same brain regions that responded to motion coherence information.
