Behavioral experiments reveal effects of stimulus complexity on working memory performance

Behavioral experiments reveal effects of stimulus complexity on working memory performance

Investigating the impact of stimulus complexity on working memory

Working memory is a crucial cognitive function that allows us to temporarily hold and manipulate information in our minds. It plays a vital role in various daily activities, such as decision-making, problem-solving, and learning. Understanding the factors that influence working memory performance is of great interest to researchers in the field of cognitive psychology. In a recent series of behavioral experiments, scientists sought to investigate the effect of stimulus complexity on working memory performance. The results shed light on how the complexity of stimuli can impact our ability to remember and process information.

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Experiment 1: Discrimination between complex and simple stimuli

In the first experiment, researchers aimed to determine whether animals could discriminate equally well between complex and simple stimuli. The animals were trained to associate each stimulus with either a left or right response key. The results showed no significant difference in performance between complex and simple stimuli in the non-delayed condition. This indicated that both stimulus classes could be successfully associated with their corresponding choice if no working memory component was present. However, when a delay was introduced, a significant performance drop was observed for simple stimuli compared to complex stimuli. This suggests that stimulus complexity plays a role in working memory performance.

Experiment 2: Controlling for spatial memory effects

To control for potential spatial memory effects or motor preparation strategies, the second experiment replaced the spatially fixed response associations with randomly presented color associations. The target location for the upcoming choice could no longer be predicted by the animals. The results mirrored those of the first experiment, with complex stimuli being maintained more accurately over time compared to simple stimuli. This finding suggests that the ability to maintain complex stimuli in working memory is not solely dependent on spatial memory or motor preparation strategies.

Experiment 3: Modulating reward contingencies

In the third experiment, researchers aimed to disentangle the role of perceptual differences and reward contingencies in the decline of choice behavior for simple stimuli. They manipulated the reward probabilities for complex stimuli, associating one pair of stimuli with a high reward probability and the other pair with a low reward probability. The results showed that reward probabilities affected the general ability to associate stimuli with the appropriate choice, but they did not account for the difference in the effect of delay performance between complex and simple stimuli. This suggests that stimulus complexity itself, rather than reward contingencies, is a key factor in working memory performance.

Neural recordings in the NCL reveal coding differences

To gain insights into the neural mechanisms underlying the observed behavioral effects, researchers recorded single neuron activity in the Nucleus Entopenduncularis Caudalis (NCL) while animals performed the delayed condition of experiment 3. The analysis revealed distinct neural activation patterns for different task parameters. Choice-related activity was found extensively in the NCL, but its extent differed notably between complex and simple stimuli. Value-related activity was predominantly observed during the sample phase for complex stimuli, while stimulus-related activity was more prevalent for complex stimuli compared to simple stimuli. These findings suggest that the NCL plays a role in representing and processing different aspects of working memory.

Temporal dynamics of neural activation schemes

Further analysis of individual neurons revealed dynamic changes in their activity patterns from the sample phase to the delay phase. Neurons in the NCL demonstrated multiplexing, switching from stimulus, value, or interaction activity to choice-related activity. This coding scheme was primarily observed when complex stimuli were presented, while simple stimuli elicited choice-related activity from the beginning. The activity levels of neurons representing choice degraded over the delay phase for simple stimuli but remained stable for complex stimuli. This suggests that the NCL is involved in dynamically representing and processing different aspects of working memory, depending on the complexity of the stimuli.

Conclusion

The results of these behavioral experiments and neural recordings provide valuable insights into the effects of stimulus complexity on working memory performance. The findings suggest that stimulus complexity plays a crucial role in our ability to remember and process information. Complex stimuli are maintained more accurately in working memory compared to simple stimuli, and the neural mechanisms involved in representing and processing complex stimuli differ from those involved in processing simple stimuli. These findings contribute to our understanding of working memory and have implications for various fields, including cognitive psychology, neuroscience, and education.