Object individuation and compensation in healthy aging.

Theories on neural compensation suggest that aged participants overactivate the brain areas involved in a task to compensate for the age-related decline. In this electrophysiological study, we investigated the temporal locus of neural overactivation in aging during multiple target processing. We measured performance and three event-related brain potential responses (N1, N2pc, and contralateral delay activity) in young and old adults, while they enumerated a variable number (1-4) of targets presented in an easy (distractor absent) or difficult (distractor present) condition.

Electrophysiological Correlates of Subitizing in Healthy Aging.

To understand the nature of age-related changes in enumeration abilities we measured two ERP responses -N2pc and CDA, associated respectively to attentive individuation and VWM- and posterior alpha band (8-15 Hz) event-related desynchronization (ERD), traditionally linked to enhanced target processing. Two groups of old and young participants enumerated a variable number (1-6) of targets presented among distractors. Older participants were less accurate in enumerating targets.

Individual differences in perceptual abilities predict target visibility during masking.

Many studies have shown that the visual system can implicitly process a single stimulus under conditions of low visibility. However, it remains unknown whether this ability extends when viewing conditions become more difficult, and whether differences in early perceptual abilities modulate masking sensitivity. To address these issues, participants enumerated a variable number of target elements among distracters in two electroencephalography experiments.

Brain dynamics of attention and working memory engagement in subitizing.

This study addressed the engagement of attention and working memory, as inferred from electrophysiological measurements, in the processing of small sets of objects. We recorded N2pc and CDA, two lateralized components of the EEG signal associated respectively with individuation and visual working memory, while participants enumerated a variable number (1-9) of uniquely colored targets among distractors. Behavioral results showed a clear subitizing effect, with lower error rates for smaller (1-3 targets) than larger sets.

Multiple object individuation during numerical Stroop.

To investigate whether semantic information relative to numbers is retained during multiple object individuation, we recorded N2pc--a neural measure of selection/individuation--during a numerical version of the Stroop task. Participants enumerated a varying number of target digits (1 to 4) whose identity was either congruent or incongruent with their numerosity. N2pc amplitudes increased as a function of target numerosity but were little affected by congruency, suggesting that multiple object individuation is a prenumeric stage that does not encode for the number magnitude of the numerosity of the individuated objects.

Multiple object individuation and exact enumeration.

Exact computation of numerosity requires the selective individuation of the elements to be enumerated so that each element is counted once and only once. Such a mechanism should operate not only when the elements to be enumerated are presented in isolation but also when they are presented in cluttered scenes. To uncover the electrophysiological correlates of the level of object representation necessary for exact enumeration, we examined ERP measures during the execution of a target enumeration task.

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.

Unconscious numerical priming despite interocular suppression.

Whether high-level properties of stimuli rendered invisible by interocular competition can influence perception and behavior remains controversial. We studied whether suppressed and invisible symbolic and nonsymbolic numerical stimuli can elicit priming. First, we established that participants were objectively unable to discriminate numerical prime stimuli when interocular suppression rendered them invisible.