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Biomedical subjects

John Zhu

Publications and source records attributed to John Zhu.

5 recordsLinked to original sources
PubMed2006

Looking for answers: eye movements in non-visual cognitive tasks.

It is not known why people move their eyes when engaged in non-visual cognition. The current study tested the hypothesis that differences in saccadic eye movement rate (EMR) during non-visual cognitive tasks reflect different requirements for searching long-term memory. Participants performed non-visual tasks requiring relatively low or high long-term memory retrieval while eye movements were recorded. In three experiments, EMR was substantially lower for low-retrieval than for high-retrieval tasks, including in an eyes closed condition in Experiment 3. Neither visual imagery nor between-task difficulty was related to EMR, although there was some evidence for a minor effect of within-task difficulty. Comparison of task-related EMRs to EMR during a no-task waiting period suggests that eye movements may be suppressed or activated depending on task requirements. We discuss a number of possible interpretations of saccadic eye movements during non-visual cognition and propose an evolutionary model that links these eye movements to memory search through an elaboration of circuitry involved in visual perception.

Analysis of Variance↗
PubMed2005

Differential effects of practice on the executive processes used for truthful and deceptive responses: an event-related brain potential study.

Behavior and event-related potentials (ERP) were recorded while participants made truthful and deceptive responses about previously memorized words under three instructional conditions: consistent truthful, consistent deceptive, and random deceptive. To determine if practice affected the deception-related activity we reported previously [R. Johnson, Jr., J. Barnhardt, J. Zhu, The deceptive response: effects of response conflict and strategic monitoring on the late positive component and episodic memory-related brain activity. Biol. Psychol., 64 (2003) 217-253; R. Johnson, Jr., J. Barnhardt, J. Zhu, The contribution of executive processes to deceptive responding. Neuropsychologia, 42 (2004) 878-901], participants performed two blocks of 145 trials of each condition. In the consistent truthful condition, practice benefited performance as indicated by decreased reaction time (RT) and RT variability. In addition, practice increased P300 amplitude and decreased the amplitude of a medial frontal negativity (MFN), which is believed to index the use of response-monitoring processes. However, a different pattern of results obtained in the two deception conditions. Although practice decreased RTs by almost as much as in the consistent truthful condition, the extent to which deceptive response in both conditions were slower than those in the consistent truthful condition actually increased slightly. Hence, the component of RT reflecting processing of conflicting response information did not decrease. In accord with the RT results, MFN amplitudes in the consistent deceptive and random deceptive conditions were unaffected by practice, suggesting that the amount of executive processes required to make and/or monitor deceptive responses was undiminished by practice. Although P300 amplitude increased slightly in the consistent deceptive condition, there was no change in the random deceptive condition. Thus, a major finding here is that, unlike truthful responses, the conceptually driven response conflicts underlying deceptive responses appear to be as resistant to practice-induced changes as described previously for perceptually driven response conflicts.

Adult↗
PubMed2004

The contribution of executive processes to deceptive responding.

We measured behavioral responses (RT) and recorded event-related brain potentials (ERPs) when participants made truthful and deceptive responses about perceived and remembered stimuli. Participants performed an old/new recognition test under three instructional conditions: Consistent Truthful, Consistent Deceptive and Random Deceptive. Compared to Consistent Truthful responses, Consistent Deceptive responses to both perceived and remembered stimuli produced the same pattern of less accurate, slower and more variable responses and larger medial frontal negativities (MFN). The MFN is thought to reflect activity in anterior cingulate cortex, a brain area involved in monitoring actions and resolving conflicting response tendencies. The Random Deceptive condition required participants to strategically monitor their long-term response patterns to accommodate a deceptive strategy. Even compared to the Consistent Deceptive condition, RTs in the Random Deceptive condition were significantly slower and more variable and MFN activity increased significantly. MFN scalp distribution results revealed the presence of three different patterns of brain activity; one each for truthful responses, deceptive responses and strategic monitoring. Thus, the data indicate that anterior cingulate cortex plays a key role in making deceptive responses.

Adolescent↗
PubMed2003

The deceptive response: effects of response conflict and strategic monitoring on the late positive component and episodic memory-related brain activity.

The cognitive processes and neural mechanisms underlying deceptive responses were studied using behavioral responses (RT) and event-related brain potentials (ERPs) while participants made truthful and deceptive responses about perceived and remembered stimuli. Memorized words were presented in a recognition paradigm under three instructional conditions: Consistent Truthful, Consistent Deceptive, Random Deceptive. Responses that conflicted with the truth about both perceived and remembered items produced the same pattern of slower RTs and decreased LPC amplitudes. When long-term response patterns were monitored, RTs became much slower and LPC amplitudes decreased greatly. The different behavioral and ERP changes in the two deception conditions suggested that two dissociable executive control processes, each requiring additional processing resources, can contribute to deceptive responses. The parietal episodic memory (EM) effect, thought to reflect recollection, was unaffected by whether participants responded truthfully or deceptively suggesting that it provides a measure of guilty knowledge.

Adolescent↗