The present work is an attempt to investigate the notion of roots in Amazigh (Berber), more particularly in Tashlhit from a theoretical and a psycholinguistic perspective, contributing to the debate on two views on morphological theory: the root-based and the word-based. The study aims particularly to explore whether the root is a significant morphological unit in the Tashlhit lexicon, on the one hand, and to provide further arguments against the exclusive consonantality of roots in Tashlhit, on the other. With this end in view, we tried to investigate the lexical properties of root structure in Tashlhit by distinguishing between two types of roots, the vocalic and the consonantal. At the theoretical level, the analysis is carried out under the premises of Optimality Theory (Prince and Smolensky, 1993/2004; McCarthy and Prince, 1993, 1995). Facts from the verbal and nominal morphology of the language are presented to account for the linguistic system of the language through constraint ranking. At the psycholinguistic level, we followed the assumption that linguistic phenomena are not exempt from extralinguistic factors (Berent & Shimron, 1997, 2003; Frish & Zawaydeh, 2001; Prunet, Béland & Idrissi, 2000). More specifically, we discussed data from auditory supraliminal priming experiments, based on measuring the reaction times of the participants. The results of our theoretical and empirical analyses show that the root is an essential morphemic unit which plays an important role in the understanding of language processing. We proved that roots in Tashlhit, similarly to semantic features, have some psycholinguistic reality and, hence, they have significant implications for the organization of the Tashlhit lexicon. Only phonological properties did not facilitate lexical access, leading to the conclusion that phonology has no role in word recognition processes in Tashlhit. In addition, we provided arguments in favor of the coexistence of both consonantal and vocalic roots in the Tashlhit lexicon.