Two patients undergo audiometry for hearing loss. Patient A shows a characteristic notch at 4 kHz with air and bone conduction equally affected, normal thresholds at 250–2000 Hz, and elevated thresholds at 4 kHz (40 dB HL) that improve slightly at 8 kHz (35 dB HL). Patient B shows a gradually rising audiogram with thresholds normal at 250 Hz (10 dB HL) and progressively elevated toward high frequencies (8 kHz = 60 dB HL), with air-bone gap of 25 dB at all frequencies. Which finding best distinguishes noise-induced hearing loss from otosclerosis in these two patients?