Giovanni Anobile, Francesco Tomaiuolo, Serena Campana, Guido Marci Cicchini

Three-systems for visual numerosity: a single case study

European Workshop on Cognitive Neuropsychology EWCN 2020

26-31/01/2020 Bressanone


https://doi.org/10.1016/j.neuropsychologia.2019.107259 Download

Introduction: Humans possess the capacity to assess the numerosity of a set of items over a wide range of conditions, from a handful to hundreds of items. Recent evidence shows that judgments over such a large range is facilitated by three separate mechanisms, each tuned to a specific range [1]. One means of dissociating the three mechanisms is attention: when healthy adults are asked to perform concurrently a taxing task, the judgments of low numerosities (<4 dots) and also high numerosities is affected greatly, but not intermediate numerosities [2]. Here we bring evidence from a neuropsychological perspective. We measured numerosity performance in PA, a 41-year-old patient who suffers a profound visual attentional deficit after a hypoxic brain injury. Methods: We psychophysically measured numerosity discrimination, object-distance discrimination and visual attention performance in healthy adults and in a 41-year-old patient (PA) who suffered from hypoxic insult due to a heart attack. Discrimination of numerosity and object-distance were indexed by thresholds measured in two alternative forced choice. Visual attention was measured by percent of correct choices on a multiple object tracking task. Statistical differences between accuracy rates and chance level in the Multiple Object Tracking were computed by binomial tests. Statistical differences on accuracy levels between PA and controls were calculated by Chisquare tests. The statistical differences on discrimination thresholds (WF) were calculated by a bootstrap technique. Results: PA showed a profound deficit in attentive tracking of objects over space and time (multiple object tracking), even in very simple conditions where typical participants made no errors. PA also showed a massive deficit on sensory thresholds when comparing dot-arrays containing extremely low (3 dots) or extremely high (64, 128 dots) numerosities as well as in comparing objects-distances. Surprisingly, PA discrimination thresholds were relatively spared for intermediate numerosities (12 and 16 dots). Discussion: We recently suggested that numerosity is processed by three mechanisms: 1) an attentional subitizing system working for low numerosities, up to about four; 2) a relatively attentional free estimation system, working at intermediate numerosities; and 3) an attentiondependent texture-density system coming into play for extremely high numerosities1-2. Here we tested the model from a neuropsychological perspective by measuring numerosity performance in a single patient (PA) suffering profound attentional losses after a hypoxic insult. Overall, PA deficit on the numerosity task is a U-shape function across numerosity levels which, combined with the attentional deficit, confirms the three-systems model for numerosity perception. References : 1. Anobile, G., et. al. Perception. (2016). 45, 5-31 2. Pomè, A., et. al. Atten Percept Psychophys. (2019) 81, 2604-2611