Individuation of multiple targets during visual enumeration: new insights from electrophysiology

Visual enumeration of small numerosities critically depends on the capacity of our visual system to process multiple objects as distinct entities. We assessed the functioning of this mechanism-individuation-during computation of quantities in cluttered scenes by using ERP measures. Participants saw a variable number of targets (1, 3, 5, 7) presented among distracters, and reported their quantities. Results showed that the N2pc amplitude was modulated by target numerosity and reached a plateau at five elements, in line with the supposed limit of the individuation mechanism. In addition, the N2pc asymptote varied depending on participants' enumeration efficiency, being smaller in participants with poor enumeration performance. The results indicate that computation of small quantities is based on multiple object individuation and suggest that individual neural differences during simultaneous individuation are strongly associated with enumeration performance.