Serial dependence in numerosity perception

Our conscious experience of the external world is remarkably stable and seamless, despite the intrinsically discontinuous and noisy nature of sensory information. Serial dependencies in visual perception—reflecting attractive biases making a current stimulus to appear more similar to previous ones—have been recently hypothesized to be involved in perceptual continuity. However, while these effects have been observed across a variety of visual features and at the neural level, several aspects of serial dependence and how it generalizes across visual dimensions is still unknown. Here we explore the behavioral signature of serial dependence in numerosity perception by assessing how the perceived numerosity of dot-array stimuli is biased by a task-irrelevant “inducer” stimulus presented before task-relevant stimuli. First, although prior work suggests that numerosity perception starts in the subcortex, the current study rules out a possible involvement of subcortical processing in serial dependence, confirming that the effect likely starts in the visual cortex. Second, we show that the effect is coarsely spatially localized to the position of the inducer stimulus. Third, we demonstrate that the effect is present even with a stimulus presentation procedure minimizing the involvement of post-perceptual processes, but only when participants actively pay attention to the inducer stimulus. Overall, these results provide a comprehensive characterization of serial dependencies in numerosity perception, demonstrating that attractive biases occur by means of spatially localized attentional modulations of early sensory activity

Experiential Effects on the Neural Substrates of Visual Word and Number Processing.

Visual processing of words and numbers is a uniquely human cognitive ability. Evidence suggests that a region in left occipitotemporal cortex, the so-called visual word form area (VWFA), is crucially involved in this ability, particularly in the visual recognition of words. In this dissertation, I present a methodological study and two empirical studies to investigate the role of experience in shaping the VWFA, to explore ways to estimate the amount of this experiential influence, and to examine how the neural substrates of visual number recognition are different from those of visual letter recognition. In the first study, I develop a novel statistical method to efficiently estimate correlation between paired spatial processes, and hence heritability in patterns of activation in neuroimaging datasets. The results demonstrate that the proposed method provides a better estimate of correlation and heritability than conventional voxelwise or region of interest methods. The second study applies this method in a monozygotic twin sample to explore the role of unique environmental effects in shaping VWFA activation. The results demonstrate that there are greater unique environmental effects for neural activity associated with familiar word recognition than with unfamiliar word recognition. The last study investigates whether the VWFA is also the crucial site for visual number recognition or whether number recognition is neurally dissociable from word recognition. I demonstrate letter-selective activation in left occipitotemporal cortex and number-selective activation in right lateral occipital cortex, thus establishing double dissociation. Furthermore, I show that individual differences in the laterality of visual number activation can be explained by individual differences in the laterality of numerical processing activation in parietal cortex. In sum, this dissertation investigates experiential effects on the neural substrates of visual word and number processing. In a methodological study, I present a more powerful statistical method to estimate correlation and heritability in neuroimaging datasets. The findings from the two empirical studies suggest a critical role of environment in shaping the VWFA, demonstrate a novel double dissociation between the neural substrates of letter and number recognition, and provide evidence that top-down influences give rise to the functional neural organization for visual number recognition.Ph.D.PsychologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/86434/1/joonkoo_1.pd

Investigating Unique Environmental Contributions to the Neural Representation of Written Words: A Monozygotic Twin Study

The visual word form area (VWFA) is a region of left inferior occipitotemporal cortex that is critically involved in visual word recognition. Previous studies have investigated whether and how experience shapes the functional characteristics of VWFA by comparing neural response magnitude in response to words and nonwords. Conflicting results have been obtained, however, perhaps because response magnitude can be influenced by other factors such as attention. In this study, we measured neural activity in monozygotic twins, using functional magnetic resonance imaging. This allowed us to quantify differences in unique environmental contributions to neural activation evoked by words, pseudowords, consonant strings, and false fonts in the VWFA and striate cortex. The results demonstrate significantly greater effects of unique environment in the word and pseudoword conditions compared to the consonant string and false font conditions both in VWFA and in left striate cortex. These findings provide direct evidence for environmental contributions to the neural architecture for reading, and suggest that learning phonology and/or orthographic patterns plays the biggest role in shaping that architecture

A neural basis for the visual sense of number and its development: A steady-state visual evoked potential study in children and adults

While recent studies in adults have demonstrated the existence of a neural mechanism for a visual sense of number, little is known about its development and whether such a mechanism exists at young ages. In the current study, I introduce a novel steady-state visual evoked potential (SSVEP) technique to objectively quantify early visual cortical sensitivity to numerical and non-numerical magnitudes of a dot array. I then examine this neural sensitivity to numerical magnitude in children between three and ten years of age and in college students. Children overall exhibit strong SSVEP sensitivity to numerical magnitude in the right occipital sites with negligible SSVEP sensitivity to non-numerical magnitudes, the pattern similar to what is observed in adults. However, a closer examination of age differences reveals that this selective neural sensitivity to numerical magnitude, which is close to absent in three-year-olds, increases steadily as a function of age, while there is virtually no neural sensitivity to other non-numerical magnitudes across these ages. These results demonstrate the emergence of a neural mechanism underlying direct perception of numerosity across early and middle childhood and provide a potential neural mechanistic explanation for the development of humans’ primitive, non-verbal ability to comprehend number. Keywords: Numerosity, Steady-state visual evoked potential, Child development, Visual cortex, Approximate number syste

Approximate arithmetic training tasks (Park & Brannon, 2013, 2014)

Matlab Psychtoolbox scripts for the training tasks used in the following two studies: Park J, Brannon EM (2013). Psychological Science 24(10): 2013-2019; Park J, Brannon EM (2014). Cognition 133(1): 188-200

Flawed stimulus design in additive-area heuristic studies

In a series of recently published studies purportedly on the “additive-area heuristic,” Yousif & Keil (2019; 2020) argue for a systematic distortion in the perception of the cumulative area of an item array and further claim that previous findings of numerical cognition and magnitude perception in general are “at risk” (Yousif & Keil, 2021). This commentary describes serious stimulus design flaws present in all of Yousif and colleagues experiments that prevent from making such conclusions. Specifically, item arrays used in those studies demonstrate a skewed correlational structure between selected magnitude dimensions and exhibit unbalanced ranges across different magnitude dimensions of interest. Because the perception of magnitude dimensions interferes one another and because our perceptual system is sensitive to the statistical regularities of the sensory input, such a biased design makes it difficult, if not impossible, to interpret the choice behavior of an observer making magnitude judgments. By re-introducing the mathematical framework for a systematic construction of dot array stimuli (DeWind et al., 2015) and by re-analyzing the data from another recent study on area perception (Tomlinson et al., 2020), this paper explains—and introduces a MATLAB code for—an optimal method for designing and constructing dot arrays for magnitude perception studies