A Biologically-Plausible Cognitive Model (BPCM) of Positive and Negative Congruency Effects in Masked Priming

A Biologically-Plausible Cognitive Model (BPCM) of Positive and Negative Congruency Effects in Masked Priming Ahmad Sohrabi (asohrabi@connect.carleton.ca) Depart ment of Psychology, University of Ku rdistan, Pasdaran Blvd. Sanandaj, Kurd istan, 66177 15175 Iran Robert L. West (robert_west@carleton.ca) Institute of Cognitive Science, Carleton University, 1125 Colonel By Drive Ottawa, Ontario K1S 5B6 Canada Abstract longer, responses have to be selected during the subsequent inhibitory phase. This is reflected as a late decrease in ERP for congruent compared to incongruent trials, and this should be demonstrated as a negative effect (i.e., NCE). In these studies, the reduction in ERP activ ity has been attributed to a motor self-inhibit ion, causing the NCE effect. The mask causes this inhibition to be reversed, by removing the sensory evidence for the corresponding response and init iating its suppression. The previous model of PCE and NCE (Bowman et al., 2006) depends on motor self-inhib ition and does not show a decline in NCE and overall Reaction Times (RTs) through time and shows a huge PCE eventually at very long SOAs. However, hu man data shows that NCE decreases and disappears or turns into a very small PCE at very long SOAs. The current model does show these effects and does not depend on motor self-inhib ition, but it works through attentional modulation driven by conflict. The same model that shows the PCE with strong prime and target and NCE with weak prime and target, without any changes in the parameters, shows a PCE at short mask-target SOA and an NCE at long mask-target SOA. It also shows the effect of other factors such as degradation (Schlaghecken & Eimer, 2002), mask density (Eimer & Schlaghecken, 2002), and prime duration (Eimer & Schlaghecken, 2002). The model is based on previous models that have been used to simu late different tasks such as target detection and simp le decisions in monkeys and humans (Gilzenrat et al., 2002; Usher & Davelaar, 2002; Nieuwenhuis, et al., 2005). Studies have shown a positive priming effect with a short time between the prime and the target. The prime increases the performance on the target if they are congruent and decreases the performance when they are incongruent. Paradoxically, a negative priming effect has been found with a long time between the prime and the target. A major hypothesis argues that the prime initiates a motor self-inhibitory process that causes these effects. This hypothesis has been criticized and the model based on this hypothesis does not fit human data. A model was developed that fits the human data. It depends on attentional neuro-modulation not motor self-inhibition. Keywords: M asked priming; Negative con gruency effect; modelling; attention; conflict. Introduction In masked priming tasks, a brief masked stimu lus (the prime) can affect the processing of the stimu lus that follows (the target). A prime, a mask, and a target are presented sequentially and the task is to make a decision on the target. The result is usually a Positive Congruency Effect (PCE), also known as the positive compatibility effect. In PCE, the prime increases the performance on the target if they are congruent and decreases the performance if they are incongruent (Dehaene et al., 1998; Schlaghecken & Eimer, 2000). Conversely, a negative priming effect has been found, called the Negative Congruency Effect (NCE). This effect is also known as the negative compatibility effect, where paradoxically the prime increases the performance on the target if they are incongruent and decreases the performance if they are congruent (e.g., Schlaghecken & Eimer, 2000, 2002; Eimer & Schlaghecken, 1998; Jaśkowski & Ślosarek, 2006). The PCE has been shown with a short mask-target Stimu lus Onset Asynchrony (SOA ), while the NCE has been shown main ly with a longer mask-target SOA (e.g., 100 ms). To explain these results, some researchers (Schlaghecken & Eimer, 2000; Bowman et al., 2006), based on Event Related Potential (ERP) measurements and computational modelling, argue that when SOA is short, response selection can already take place during the initial response activation phase; this is reflected as an early increase in ERP for the congruent compared to incongruent trials, and this should result in the congruency effects in the form of a PCE. When SOA is The Cur rent M odel Modeling met hods. The processing elements in the model are a few neurons with self-excitation, lateral inhibit ion, and accumulat ive activation that have a strong computational power in simu lating basic neural and cognitive processes (e.g., Usher & Davelaar, 2002; Gilzenrat et al., 2002). It has been demonstrated that these types of reduced models can resemble the neural computation of a large group of neurons (e.g., Wong & Wang, 2006). The model (Figure 1) is a mult i-layer dynamic neural model that consists of a feed-forward component for perceptuo-motor processing from the Input Layer (IL) to an intermediate layer, called Representation Layer (RL), and fro m there to the Cognitive Layer (CL) and Motor Layer