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1. General object-based features account for letter perception

   https://doi.org/10.1371/journal.pcbi.1010522  

   Janini, Daniel; Hamblin, Chris; Deza, Arturo; Konkle, Talia (September 2022, PLOS Computational Biology)

   Isik, Leyla (Ed.)

   After years of experience, humans become experts at perceiving letters. Is this visual capacity attained by learning specialized letter features, or by reusing general visual features previously learned in service of object categorization? To explore this question, we first measured the perceptual similarity of letters in two behavioral tasks, visual search and letter categorization. Then, we trained deep convolutional neural networks on either 26-way letter categorization or 1000-way object categorization, as a way to operationalize possible specialized letter features and general object-based features, respectively. We found that the general object-based features more robustly correlated with the perceptual similarity of letters. We then operationalized additional forms of experience-dependent letter specialization by altering object-trained networks with varied forms of letter training; however, none of these forms of letter specialization improved the match to human behavior. Thus, our findings reveal that it is not necessary to appeal to specialized letter representations to account for perceptual similarity of letters. Instead, we argue that it is more likely that the perception of letters depends on domain-general visual features. 

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2. Friends in low-entropy places: Letter position influences orthographic neighbor effects in visual word identification

   Luthra, S.; Magnuson, J. S. (July 2018, Proceedings of the Cognitive Science Society)

   In visual word recognition, having more orthographic neighbors (words that differ by a single letter) generally speeds access to a target word. But neighbors can mismatch at any letter position. In light of evidence that information content varies between letter positions, we consider how neighbor effects might vary across letter positions. Results from a word naming task indicate that response latencies are better predicted by the relative number of positional friends and enemies (respectively, neighbors that match the target at a given letter position and those that mismatch) at some letter positions than at others. In particular, benefits from friends are most pronounced at positions associated with low a priori uncertainty (positional entropy). We consider how these results relate to previous accounts of position-specific effects and how such effects might emerge in serial and parallel processing systems. 

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3. Raeding with the fingres: Towards a universal model of letter position coding

   https://doi.org/10.3758/s13423-022-02078-0  

   Baciero, Ana; Gomez, Pablo; Duñabeitia, Jon Andoni; Perea, Manuel (June 2022, Psychonomic Bulletin & Review)

   Abstract Letter position coding in word recognition has been widely investigated in the visual modality (e.g., labotarory is confusable with laboratory), but not as much in the tactile modality using braille, leading to an incomplete understanding of whether this process is modality-dependent. Unlike sighted readers, braille readers do not show a transposed-letter similarity effect with nonadjacent transpositions (e.g., labotarory = labodanory; Perea et al., 2012). While this latter finding was taken to suggest that the flexibility in letter position coding was due to visual factors (e.g., perceptual uncertainty in the location of visual objects (letters)), it is necessary to test whether transposed-letter effects occur with adjacent letters to reach firm conclusions. Indeed, in the auditory modality (i.e., another serial modality), a transposed-phoneme effect occurs for adjacent but not for nonadjacent transpositions. In a lexical decision task, we examined whether pseudowords created by transposing two adjacent letters of a word (e.g., laboartory) are more confusable with their base word (laboratory) than pseudowords created by replacing those letters (laboestory) in braille. Results showed that transposed-letter pseudowords produced more errors and slower responses than the orthographic controls. Thus, these findings suggest that the mechanism of serial order, while universal, can be shaped by the sensory modality at play. 

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4. Set Size Effects on the P3b in a BCI Speller

   D'Amico, Alessandro; de Sa, Virginia R. (January 2022, Proceedings of the Annual Conference of the Cognitive Science Society)

   Culbertson, J; Perfors, A.; Rabagliati, H.; Ramenzoni, V. (Ed.)

   Data were collected from a brain-computer interface speller that utilized the P3b as a control signal. Stimuli consisted of letters and their “segments”. Importantly, different letters were made up of different numbers of segments from a 10 segment library. Subjects were instructed to mentally note whenever segments from their letter (targets) were flashed. We found that P3b amplitudes of target segments decreased as the number of segments in a letter (target letter complexity) increased.In contrast, the P3b attenuation was not affected by the total number of letters a segment belonged to (segment frequency).These results may reflect higher task difficulty caused by increased working memory load with increased target letter complexity. Alternatively, it’s possible that despite the target rate being fixed at 30% within each block, subjects erroneously believed the target rate increased with target letter complexity.Further work to disentangle these possibilities may enrich our understanding of the P3b. 

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5. Friends in Low‐Entropy Places: Orthographic Neighbor Effects on Visual Word Identification Differ Across Letter Positions

   https://doi.org/10.1111/cogs.12917  

   Luthra, Sahil; You, Heejo; Rueckl, Jay G.; Magnuson, James S. (December 2020, Cognitive Science)

   Abstract Visual word recognition is facilitated by the presence oforthographic neighborsthat mismatch the target word by a single letter substitution. However, researchers typically do not considerwhereneighbors mismatch the target. In light of evidence that some letter positions are more informative than others, we investigate whether the influence of orthographic neighbors differs across letter positions. To do so, we quantify the number ofenemiesat each letter position (how many neighbors mismatch the target word at that position). Analyses of reaction time data from a visual word naming task indicate that the influence of enemies differs across letter positions, with the negative impacts of enemies being most pronounced at letter positions where readers have low prior uncertainty about which letters they will encounter (i.e., positions with low entropy). To understand the computational mechanisms that give rise to such positional entropy effects, we introduce a new computational model, VOISeR (Visual Orthographic Input Serial Reader), which receives orthographic inputs in parallel and produces an over‐time sequence of phonemes as output. VOISeR produces a similar pattern of results as in the human data, suggesting that positional entropy effects may emerge even when letters are not sampled serially. Finally, we demonstrate that these effects also emerge in human subjects' data from a lexical decision task, illustrating the generalizability of positional entropy effects across visual word recognition paradigms. Taken together, such work suggests that research into orthographic neighbor effects in visual word recognition should also consider differences between letter positions. 

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