Recordings

Well-isolated extracellular action potentials of single IT cortex neurons were recorded with tungsten microelectrodes. The electrode was lowered with a Narishige microdrive through a guide tube that was fixed in a Crist grid. Recordings were made using a Plexon data acquisition system. Spiking activity was thresholded on-line and spike waveforms were saved at 40 kHz. Spikes were sorted when necessary and single-unit isolation was verified using Offline Sorter (Plexon).

Eye position was measured on-line with an infrared-based eye-tracking system (EC-240A, ISCAN; 120 Hz sampling rate). The analog eye-movement signal was saved with a sampling frequency of 1 kHz. Eye positions, stimulus events, and behavioral events were recorded simultaneously with spiking activity and stored for later off-line analysis on a computer synchronized with the Plexon data acquisition system.