Figure 1.

(A) Behavioral performance at a task in which subjects had to identify and temporally order rapidly successive brief (20-ms duration) tonal stimuli that in some trials did, and in other trials did not, differ in frequency. Performance was defined during MEG recording sessions conducted for poor readers and controls (10–12). The normal readers in the control group performed this task with almost no errors. Poor readers (see Methods for subject selection) made many errors, even at long (500-ms) ISIs. All poor readers performed better at longer than at shorter ISIs. (B) Examples of evoked magnetic responses recorded in the 37 channels centered on left hemisphere auditory cortex, averaged from ≈100 artifact-free presentation of stimulus-pairs at 200-ms ISI in a control subject. The timing of stimulus events is indicated in green. (C–E) Examples of rms waveforms computed across sensors at each time sample for three different control subjects, for tonal stimulus pairs presented with 200-ms ISIs. Stimulus events are indicated in green. Small vertical arrows mark the 100-ms poststimulus time (the time of occurrence of the expected evoked M100 response) for the initial and the second stimulus of the pair. (F) Example of evoked magnetic field response for a 200-ms ISI condition for a poor-reading subject. Whereas a normal-strength response was evoked by the first stimulus, the second rapidly successive stimulus evoked only a weak response. (G–I) Example rms waveforms from three poor-reading subjects.