Humans use inferred statistical properties of sequential events to smoothen subsequent actions by anticipatory movements. These anticipatory movements have been studied in the serial reaction time ...Show moreHumans use inferred statistical properties of sequential events to smoothen subsequent actions by anticipatory movements. These anticipatory movements have been studied in the serial reaction time (SRT) task, in which participants anticipate the target stimuli in learned sequences, however, under uncertainty, the participants seem to adhere to a centering strategy. It remains unclear whether this centering behavior is a statistically inferred way to compensate for the absence of sequence knowledge, using the center as an optimal anticipatory position. In this study, two state-of-the-art Deep Reinforcement Learning (Deep RL) algorithms (Proximal Policy Optimization (PPO) & Soft Actor-Critic (SAC)) are compared and employed to train artificial agents to investigate the scope of centering behavior, by manipulating the frequency distributions of target stimuli. While SAC evidently outperformed PPO in terms of performance and stability, both algorithms displayed an effect of frequency distribution on centering position. Specifically, a proportional shift toward more probable target stimuli, suggesting that centering behavior is indeed anticipatory behavior as a way to compensate for the absence of explicit sequence knowledge.Show less
Human behaviour consists largely of elemental tasks, which when performed in sequence make up larger actions. In the trajectory serial reaction time (SRT) task, participants move their cursors to...Show moreHuman behaviour consists largely of elemental tasks, which when performed in sequence make up larger actions. In the trajectory serial reaction time (SRT) task, participants move their cursors to one of four stimuli located at corners in a square-shaped grid. This task has been used to study implicit learning of motor skills. Of interest to the present study are results from Kachergis, De Kleijn, et al. (2014) in which subsequences were not learned unilaterally. Preliminary analysis carried out after the fact suggests this effect cannot be fully ascribed to diagonal or infrequent moves making certain subsequences harder. The present study aims to determine whether the effect is due to variations in distance, whether it is correlated with frequency, and whether its orientation frame is absolute or relative. 52 participants divided into two conditions, each of which saw subsequences in a different orientation, performed an online version of the trajectory SRT task. We discuss three main findings. First, no evidence was found to suggest relative distance played a role. Second, moves which occurred frequently were associated with lower RTs. Third, relative RTs per subsequence were the same between the two conditions, indicating the effect is relative to the orientation of moves made during training. Together these results lead us to conclude that higher frequency of certain moves during training leads to better post-training performance of subsequences containing these moves. Post-hoc analyses suggest this relationship might not be entirely straight-forward. In light of these outcomes and their implications, we discuss several opportunities for future research, as well as limitations and alternate interpretations.Show less
When infants have two possible rules that they can discover in an artificial language, a prosodic rule and a structure rule, which one do they discover and does this change with development? Prior...Show moreWhen infants have two possible rules that they can discover in an artificial language, a prosodic rule and a structure rule, which one do they discover and does this change with development? Prior studies on infants’ cue weighing suggest a preference for prosodic cues for eight-month-old infants, and a preference for structure for ten-month-old infants when segmenting speech. Using a Headturn Preference Procedure with adapted stimuli from Spierings and ten Cate (2014), we compared looking times for a prosody and structure test condition. We found condition did not have a significant effect on looking time. However, ten-month-old infants had significantly longer looking times compared to the eight-month-old infants. We also found a significant difference for gender, suggesting that female infants have a preference for a different cue to discover underlying language patterns than males.Show less
Prosody and structure are important cues for infants when they are learning a language. In this thesis, I investigated which of these two cues infants of seven months old find more salient. A Head...Show moreProsody and structure are important cues for infants when they are learning a language. In this thesis, I investigated which of these two cues infants of seven months old find more salient. A Head-Turn Preference procedure was used in both Experiment 1a and Experiment 1b to see whether infants found an inconsistent prosody pattern or inconsistent structure pattern compared to a familiarized pattern more interesting. Results revealed that infants had a longer looking time for the inconsistent prosody pattern than for the inconsistent structure, which indicates a stronger interest for the inconsistent prosody. If infants have a novelty preference, which is commonly assumed, this would mean that infants rely more on prosodic cues than structural cues. Whether or not this is the case will be examined further in Experiment 2. Also the points of improvement for Experiment 1 and the design of how Experiment 2 is conducted are discussed.Show less
