This paper details a study to evaluate the effects of modified speech on perceptual speaker identification (SID) performance by naive listeners. Speech recordings made by eight male, native-French speakers were selected from the PTSVox database. The pitch and speech tempo of the recordings were modified at the word-level. The first 75% of words spoken were modified, such that the percentage of modification began at 100% and gradually decayed to 0%. The direction of the modifications was also examined, such that pitch modifications began at ±600 cents and speech tempo modifications began at a ratio of either 1:2 or 3:2 (modified to normal speech tempo). Following a familiarization period, participants completed two rounds of 48 "go/no-go" task trials (balanced), where each round corresponded to a different speech modification type. The main results showed perceptual SID performance was significantly affected when participants were presented speech recordings that contained pitch modifications in comparison to speech tempo modifications. The findings revealed participants were able to overcome higher percentages of speech tempo modifications to make correct distinctions between speakers. Although modified pitch influenced in voice perception performance, high variability between participant responses were observed, which suggests listeners model speakers differently.