Biomedical subjects

Joo-Hyun Song

Publications and source records attributed to Joo-Hyun Song.

7 recordsLinked to original sources

PubMed2006

Fixation offset facilitates saccades and manual reaching for single but not multiple target displays.

Turning off a fixation point, typically for 200 ms, before the onset of a peripheral target substantially reduces saccadic reaction times. This facilitatory effect generated by an inserted temporal gap between fixation offset and the target appearance is called the "gap" effect [J Opt Soc Am 57:1030-1033, 1967]. We show that the gap reduces the initial latency of both saccades and manual pointing in single and multiple target displays. Yet, in multiple target displays, the gap increased the movement duration because eye or hand movements were frequently misdirected toward distractors so that the trajectory had to be corrected. Thus, in spite of the shortened latency, the total time for trial completion was not shortened in multiple target displays, whereas it was reduced in single target displays. This selective gap effect for a single target was not restricted to goal-directed motor tasks because perceptual discrimination tasks, where no motor response is required, also demonstrated the gap effect only for single target displays. Our results suggest that the gap may facilitate attentional disengagement, but it does not help target selection in motor and perceptual discrimination tasks, where the allocation of attention to the target is required.

Adult↗

PubMed2006

Role of focal attention on latencies and trajectories of visually guided manual pointing.

Previous studies have shown that an odd-colored target among uniformly colored distractors can be rapidly detected and localized using broadly distributed attention over an entire display. In the current study, we show that such a broadly distributed attentional allocation is not sufficient for seemingly effortless goal-directed manual pointing. Latencies and movement durations of manual pointing in odd-colored search tasks become shorter and curved trajectories decreased as the number of distractors increase or target color repetitions increases. Because these manipulations have been shown to facilitate the deployment of narrowly focused attention to a target but not for distributed attention, this adds further support to the view that focal attention is necessary for goal-directed action. In addition, the presence of highly curved movement trajectories, directed first to a distractor then to the target reflects ongoing changes in focal attentional deployment and target selection.

Attention↗

PubMed2005

Visual working memory for simple and complex features: an fMRI study.

Visual working memory (VWM) allows us to hold visual information briefly in our minds after its disappearance. It is important for bridging the present to the immediate past. Previous neuroscience studies on VWM have shown that several parietal, frontal, and occipitotemporal brain regions subserve this function. Those studies, however, have often focused on VWM for a single property, such as color. Yet, in behavior, the capacity of VWM is sensitive to the complexity of to-be-remembered visual features. How do different brain areas represent VWM for visual features of different complexity and for combination of features? To address this question, we used functional MRI to study the response profile of several brain regions in three VWM tasks. In all tasks, subjects saw 1 to 7 colored polygons and had to remember their color (a simple feature), shape (a complex feature), or both color and shape. Behavioral performance showed that VWM reached capacity limit at about 3 colors, 2 shapes, and 2 compound objects. In the fMRI data, we found different functional profiles for frontal, parietal, and occipitotemporal regions. Specifically, the posterior parietal cortex was sensitive to both featural and VWM load manipulations. The prefrontal regions were sensitive to VWM load manipulation but relatively insensitive to featural differences. The occipitotemporal regions were sensitive to featural differences, but not to VWM load manipulation. We propose that the response properties of these regions can jointly account for several findings in human VWM behavior.

Adolescent↗

PubMed2005

Connecting the past with the present: how do humans match an incoming visual display with visual memory?

Extensive cognitive research has been devoted to the sensitivity of the visual system to invariant statistical information. For example, many studies have shown that performance improves when a visual display is presented repeatedly. But what allows humans to connect the current visual input to previous memory? Is the connection made only when the entire incoming display matches with a previous memory, or can retrieval rely on an incomplete match between the input and a learned display? Using a visual search task, we show that (1) once a repeated display is learned, subjects can retrieve it even when an incoming display only matches it in 3-4 locations; (2) however, early during learning, repetition of a small proportion of a display is not enough to establish a strong memory trace for the repeated locations. We suggest that the retrieval of a well-established visual memory can proceed even if an incoming display partly matches the previous memory.

Adolescent↗

PubMed2005

Hyperspecificity in visual implicit learning: learning of spatial layout is contingent on item identity.

Humans conduct visual search faster when the same display is presented for a 2nd time, showing implicit learning of repeated displays. This study examines whether learning of a spatial layout transfers to other layouts that are occupied by items of new shapes or colors. The authors show that spatial context learning is sometimes contingent on item identity. For example, when the training session included some trials with black items and other trials with white items, learning of the spatial layout became specific to the trained color--no transfer was seen when items were in a new color during testing. However, when the training session included only trials in black (or white), learning transferred to displays with a new color. Similar results held when items changed shapes after training. The authors conclude that implicit visual learning is sensitive to trial context and that spatial context learning can be identity contingent.

Adolescent↗

PubMed2005

Spatial context learning in visual search and change detection.

Humans conduct visual search more efficiently when the same display is presented for a second time, showing learning of repeated spatial contexts. In this study, we investigate spatial context learning in two tasks: visual search and change detection. In both tasks, we ask whether subjects learn to associate the target with the entire spatial layout of a repeated display (configural learning) or with individual distractor locations (nonconfigural learning). We show that nonconfigural learning results from visual search tasks, but not from change detection tasks. Furthermore, a spatial layout acquired in visual search tasks does not enhance change detection on the same display, whereas a spatial layout acquired in change detection tasks moderately enhances visual search. We suggest that although spatial context learning occurs in multiple tasks, the content of learning is, in part, task specific.

Adult↗

PubMed2005

High-capacity spatial contextual memory.

Humans show implicit memory for complex spatial layouts, which aids in subsequent processing of these layouts. Research efforts in the past 5 years have focused primarily on a single session of training involving a dozen repeated displays. Yet every day, people encounter many more visual layouts than were presented in such experiments. In this study, we trained subjects to learn 60 repeated displays, randomly intermixed within 1,800 nonrepeated displays, spread over 5 consecutive days. On each day, the subjects conducted visual search on 360 new displays and a new set of 12 repeated displays, each repeated 30 times. Contextual memory was observed daily. One week after the fifth session, the subjects still searched faster on the repeated displays learned previously. We conclude that the visual system has a high capacity for learning and retaining repeated spatial context, an ability that may compensate for our severe limitations in visual attention and working memory.

Adult↗