The analysis of false alarm rates proved that non-target stimuli falling at the attended location (L+) and within the target spatial frequency bandwidth (pseudo-targets) were more difficult to suppress in that they elicited an average of 8.77% of FAs.
At prefrontal sites a negative deflection (NP400) was identified in the 370 430 ms time window, which was not characteristic of target stimuli (as proved by a direct comparison with the ERPs elicited by real targets at Fpz, in Figure 3) and was much smaller in response to lures falling at an unattended location or outside the target spatial frequency bandwidth.
The fact that gratings falling at the attended location and within the target's spatial frequency bandwidth (pseudo-targets) elicited 40 times more FAs than other types of lures indicates how similar they were to targets and how difficult they were to suppress at both the cognitive and response preparation levels.
Standard stimuli as well as (infrequent) target stimuli with a different frequency bandwidth were generated by all loudspeakers, but the listeners were required to respond only to targets delivered by one specific loudspeaker.
Figure 2 shows ERP waveforms recorded over posterior scalp sites in response to lure gratings of 1.5 and 3 c/deg, sharing or not sharing space location with the target (L+ or L-) and falling or not falling within the same spatial frequency bandwidth as the target.
In fact, ERP analysis revealed strong attentional effects for intermediate frequencies (lure stimuli) presented at the attended location and falling within the same spatial frequency bandwidth as actual targets (see Figure 3).
The three section, 60 periods SWG TWT predicted peak radiation power 130 W at target frequency 94 GHz, 39.5 dB saturated gain, 5.3% instantaneous 3-dB frequency bandwidth, and 6.5% electronic efficiency.
In order to investigate the neural bases of the suppression effect for pseudo-targets, a difference wave was computed by subtracting the ERPs to lures that were less difficult to suppress (frequency-pseudorelevant (F+) but location-irrelevant (L-)) from the ERPs to pseudo-targets (location-relevant and falling within the relevant spatial frequency bandwidth).
The main objective was to achieve target impedance at the front absorber face, so as to attain maximum sound-attenuation over a wide frequency bandwidth.
The FA rate was extremely low and ranged from 0.2% to all types of non-targets (including those of the target frequency: 0.75 and 6 c/deg) to an average of 8.77% for pseudo-targets falling at the attended location (L+) and within the target spatial frequency bandwidth (F+/-), as illustrated in Figure 1 (6.63% for the attend-0.75 condition, and 10.90% for the attend-6 condition).
