For a hearing-impaired person provided with a hearing aid device with which sound acquisition ensues outside of the auditory canals of the person, the localization capability with regard to a signal source is lost. To compensate the information loss that occurs due to the acquisition of an acoustic signal outside of the auditory canals, in the signal processing in the hearing aid device of an acoustic input signal acquired by at least one microphone of the hearing aid device, the transfer function of the head or of the external ear is taken into account between the position at which the microphone is located and a position in the auditory canal of the hearing device user. The natural location capability of a person to localize a signal source in space thus is not lost given treatment with a hearing aid device that is not worn in the auditory canal.