Two stimuli were presented at varying stimulus onset asynchronies (SOAs), each associated with a speeded two-alternative discrimination task. The first stimulus was a tone at one of two possible frequencies. The second stimulus was a line drawing of a real-world concept, that was presented in black on a white background, or overlapped to a pattern mask that reduced the stimulus clarity. The tone had to be classified as a high or low pitched tone. The picture had to be classified as that of a biological or artifactual concept. Results showed a classical psychological refractory period (or PRP) effect. The reaction times to the line drawing increased as the SOA was decreased. The effects of the manipulation of masking on reaction times to the line drawing were detected at the longest SOAs, and were drastically reduced at the shortest SOAs. The results are discussed in relation to models proposed to explain the PRP effect.