Biomedical subjects

Do-Joon Yi

Publications and source records attributed to Do-Joon Yi.

7 recordsLinked to original sources

PubMed2006

Linking implicit and explicit memory: common encoding factors and shared representations.

Dissociations between implicit and explicit memory have featured prominently in theories of human memory. However, similarities between the two forms of memory have been less studied. One open question concerns whether implicit and explicit memory share encoding resources. To explore this question, we employed a subsequent memory design in which several novel scenes were repeated once during an fMRI session and explicit memory for the scenes was unexpectedly tested afterward. Subsequently remembered scenes produced more behavioral priming and neural attenuation-two conventional measures of implicit memory-than did subsequently forgotten scenes. Moreover, brain-behavior correlations between these two implicit measures were mediated by subsequent memory. Finally, tonic activity, possibly reflecting the natural time course of attention, was predictive of subsequent memory. These results suggest that implicit and explicit memory are subject to the same encoding factors and can rely on similar perceptual processes and representations.

Adolescent↗

PubMed2006

Attentional modulation of repetition attenuation is anatomically dissociable for scenes and faces.

Repeating a stimulus generally leads to a decreased response in neural activity compared to that for novel items. This neural attenuation provides a marker for stimulus-specific perceptual encoding and memory that can be detected using functional magnetic resonance imaging (fMRI). Although previously assumed to occur automatically whenever a stimulus is repeated, recent studies have begun to show that the repetition attenuation effect is task-specific and modulated by attention. Here, we demonstrate that attention is crucial for obtaining neural attenuation even after extensive stimulus repetitions. Furthermore, the effect of attention on attenuation is anatomically dissociable for stimuli that have relatively segregated neural representations in high-level perceptual cortex. To manipulate attention, we used overlapping scene and face images, and asked subjects to attend to either category. In a scene-sensitive cortical region known as the parahippocampal place area (PPA), significant attenuation in the fMRI BOLD signal was observed for the attended repeated scenes (relative to attended novel scenes), while no attenuation was observed for ignored repeated scenes or attended repeated faces against their respective novel image baselines. Conversely, in the face-sensitive region known as the fusiform face area (FFA), significant attenuation was observed for attended repeated faces, but not for ignored repeated faces or attended repeated scenes. An additional control experiment ruled out alternative explanations based on global signal level reductions due to inattention. Thus, attention actively governed when neuronal activity was attenuated to repeated perceptual input, and such attenuation was specific to the cortical regions that actively represent the attended category of stimuli.

Adaptation, Physiological↗

PubMed2005

Shape-specific perceptual learning in a figure-ground segregation task.

What does perceptual experience contribute to figure-ground segregation? To study this question, we trained observers to search for symmetric dot patterns embedded in random dot backgrounds. Training improved shape segmentation, but learning did not completely transfer either to untrained locations or to untrained shapes. Such partial specificity persisted for a month after training. Interestingly, training on shapes in empty backgrounds did not help segmentation of the trained shapes in noisy backgrounds. Our results suggest that perceptual training increases the involvement of early sensory neurons in the segmentation of trained shapes, and that successful segmentation requires perceptual skills beyond shape recognition alone.

Discrimination, Psychological↗

PubMed2005

Attentional modulation of learning-related repetition attenuation effects in human parahippocampal cortex.

Two of the most fundamental processes in biological vision are attention and learning. Attention actively selects and enhances visual information that is most relevant to behavior. Learning enables the visual system to benefit from perceptual experience. The amount of visual information to learn is infinite; however, top-down control mechanisms must somehow regulate learning to achieve an adaptive balance between plasticity and stability in neural circuitry. Functional magnetic resonance imaging (fMRI) can measure learning-related changes in neural activity to previously viewed perceptual stimuli. Described variably as the repetition suppression or adaptation effect, the attenuation in neural activity to repeated stimuli versus novel stimuli provides a marker for stimuli-specific perceptual processing and memory. One important issue concerns whether repetition attenuation is automatic or not, and recent work has begun to show that it is sensitive to task demands. Accordingly, the present study further examined how attention controls the attenuated response to repeated stimuli, specifically testing whether attention is important for initial encoding, for the expression of memory traces, or for both encoding and expression. To manipulate attention, we used overlapping scene and face images and asked subjects to attend to either category. fMRI revealed significant attenuation in the parahippocampal place area for only the repeated scenes that were attended both during the initial presentation and during repetition. Thus, attention actively governs when neuronal activity is attenuated to repeated perceptual input, and such attention is important during both initial encoding and subsequent expression of the learned information.

Adolescent↗

PubMed2004

Neural fate of ignored stimuli: dissociable effects of perceptual and working memory load.

Observers commonly experience functional blindness to unattended visual events, and this problem has fuelled an intense debate concerning the fate of unattended visual information in neural processing. Here we used functional magnetic resonance imaging (fMRI) to demonstrate that the type of task that a human subject engages in determines the way in which ignored visual background stimuli are processed in parahippocampal cortex. Increasing the perceptual difficulty of a foveal target task attenuated processing of task-irrelevant background scenes, whereas increasing the number of objects held in working memory did not have this effect. These dissociable effects of perceptual and working memory load clarify how task-irrelevant, unattended stimuli are processed in category-selective areas in human ventral visual cortex.

Adult↗

PubMed2004

The neural fate of consciously perceived and missed events in the attentional blink.

Cognitive models of attention propose that visual perception is a product of two stages of visual processing: early operations permit rapid initial categorization of the visual world, while later attention-demanding capacity-limited stages are necessary for the conscious report of the stimuli. Here we used the attentional blink paradigm and fMRI to neurally distinguish these two stages of vision. Subjects detected a face target and a scene target presented rapidly among distractors at fixation. Although the second, scene target frequently went undetected by the subjects, it nonetheless activated regions of the medial temporal cortex involved in high-level scene representations, the parahippocampal place area (PPA). This PPA activation was amplified when the stimulus was consciously perceived. By contrast, the frontal cortex was activated only when scenes were successfully reported. These results suggest that medial temporal cortex permits rapid categorization of the visual input, while the frontal cortex is part of a capacity-limited attentional bottleneck to conscious report.

Analysis of Variance↗

PubMed2003

Inhibition of return to occluded objects.

Since many visual objects are vulnerable to occlusion, an active process that tracks objects behind occluders confers considerable ecological validity to the visual system. We studied this possibility by testing whether inhibition of return can be observed with occluded objects. In our experiments, two moving objects disappeared or reappeared behind occluders while a cue and a probe were presented. Contrary to the results of a previous study (Tipper, Weaver, Jerreat, & Burak, 1994), responses were consistently delayed for the cued object that was occluded when it was cued (Experiment 1), when it was probed (Experiment 2), or both (Experiment 3). These results suggest that attention can select occluded objects that are out of view. Our findings are in line with prior studies that have demonstrated similar perceptual/attentional effects for occluded objects, as well as for visible objects.

Attention↗