Biomedical subjects

David Soto

Publications and source records attributed to David Soto.

8 recordsLinked to original sources

PubMed2006

Seeing the content of the mind: enhanced awareness through working memory in patients with visual extinction.

In the present study, we demonstrate that parietal patients with visual extinction show enhanced awareness when there is a match between the current contents of their working memory and the stimuli presented in the visual field. This effect cannot be attributed to automatic bottom-up priming from the presentation of a memory cue, because extinction was reduced only when patients committed the cue to memory, and not when primes were viewed passively or merely identified. The results suggest that reentrant processes, from working memory, modulate awareness.

Aged↗

PubMed2006

Dividing the mind: the necessary role of the frontal lobes in separating memory from search.

Working memory plays a crucial role in the control of visual selection. Previous research has shown that attentional deployment can be biased to objects in an array matching the contents of working memory. Here, we examined the role of the frontal cortex in determining the interaction between working memory and attention. At the start of each trial, participants memorized an object cue that could contain either the target or a distracter, when the object reappeared in the subsequent search array. Relative to age-matched controls, patients suffering from damage to the frontal lobes showed a stronger effect of the memory stimulus on search. Interestingly, there was an effect of frontal damage on the mean latencies to fixate targets but the effect of memory validity on the number of first saccades to the target, and their time of initiation, was similar across the groups. The results suggest that, following the earliest deployment of attention, frontal lobe structures are involved in separating relevant target from irrelevant (object cue) information, when both are held in memory.

Adult↗

PubMed2005

Working memory can guide pop-out search.

Top-down feedback from working memory (WM) can exert an early and involuntary influence on visual selection for targets that are relatively difficult to discriminate [Soto, D., Heinke, D., Humphreys, G. W., & Blanco, M. J. (2005) Journal of Experimental Psychology: Human Perception and Performance, 31, 248]. Here, we demonstrate similar effects even on search for a pop-out target. At the beginning of each trial, participants memorized a prime that could contain either the search target or a distracter in the subsequent search array. Targets and distractors were easily discriminable. Despite this, the prime in WM affected responses latencies and the direction of the first saccade. Top-down search, guided by the contents of WM, can modulate selection even when salient bottom-up cues are present.

Adolescent↗

PubMed2005

Effects of dinucleoside polyphosphates on trabecular meshwork cells and aqueous humor outflow facility.

The most important risk factor for the development of glaucoma is elevated intraocular pressure (IOP). Hypotensive drugs decrease IOP, preventing optic nerve damage and further vision loss. The balance between aqueous humor (AH) production and drainage determines IOP, and problems in AH outflow pathways are associated with open-angle glaucoma development. Previous studies have shown the presence of diadenosine tetraphosphate (Ap(4)A) and pentaphosphate (Ap(5)A) in the AH. Topic application of Ap(4)A to the cornea decreased IOP, whereas Ap(5)A increased it. Because dinucleoside polyphosphates stimulate P2Y purinergic receptors, we studied their presence in trabecular meshwork (TM) cells. Additionally, the effects of diadenosine polyphosphates (Ap(n)As; n = 3-5) and Up(4)U (P(1),P(4)-(diuridine 5')-tetraphosphate; INS365) in outflow facility were tested. P2Y(1), P2Y(2), and P2Y(4) receptors were detected in TM cells by Western blot and immunocytochemistry. In TM cells, Ap(3)A, Ap(4)A, and Ap(5)A induced discrete intracellular calcium concentration ([Ca(2+)](i)) mobilizations compared with higher and more sustained [Ca(2+)](i) mobilizations after Up(4)U application. In bovine ocular anterior segments perfused at constant pressure, 1 microM Ap(3)A or Ap(4)A increased outflow facility, whereas Up(4)U or Ap(5)A did not modify it. 2-MeSADP, a selective P2Y(1) agonist, induced outflow facility increases similar to those obtained after Ap(3)A and Ap(4)A, and these were prevented by addition of the selective P2Y(1) receptor antagonist MRS-2179 (2'-deoxy-N(6)-methyladenosine-3',5'-diphosphate). Our results demonstrate that the hypotensive effect of Ap(4)A and other dinucleotides is mediated, at least in part, by increasing trabecular outflow facility through activation of P2Y(1) receptors. The latter would seem to be an interesting target in the development of antiglaucomatous drugs to selectively increase AH outflow.

Animals↗

PubMed2005

Early, involuntary top-down guidance of attention from working memory.

Four experiments explored the interrelations between working memory, attention, and eye movements. Observers had to identify a tilted line amongst vertical distractors. Each line was surrounded by a colored shape that could be precued by a matching item held in memory. Relative to a neutral baseline, in which no shapes matched the memory item, search was more efficient when the memory cue matched the shape containing the target, and it was less efficient when the cued stimulus contained a distractor. Cuing affected the shortest reaction times and the first saccade in search. The effect occurred even when the memory cue was always invalid but not when the cue did not have to be held in memory. There was also no evidence for priming effects between consecutive trials. The results suggest that there can be early, involuntary top-down directing of attention to a stimulus matching the contents of working memory.

Adolescent↗

PubMed2004

Spatial attention and object-based attention: a comparison within a single task.

There is now much experimental evidence supporting the idea that visual attention can be deployed in at least two ways: one space-based and other object-based. However, it is not clear whether space- and object-based attention work in an integrated way within the visual system. In this article, we present two experiments in which we compare both components of attention within a cueing paradigm. Participants had to discriminate the orientation of a line that appeared within one of four moving circles, differing in colour. A cue appearing close to one of the four circles indicated the location or circle where the target stimulus was likely to appear. Spatial and object cueing effects were observed: responses were faster when target appeared either at the precued location or within the precued object. In addition, the object-cueing effect occurred only when the cue was spatially invalid and not when it was spatially valid. These results suggest that object- and space-based attention interact, with selection by location being primary over object-based selection.

Adult↗

PubMed2004

Modulation of aqueous humor outflow by ionic mechanisms involved in trabecular meshwork cell volume regulation.

PURPOSE: Trabecular meshwork (TM) cell shape, volume, contractility and their interactions with extracellular matrix determine outflow facility. Because cell volume seems essential to TM function, this study was conducted to investigate further the ionic channels and receptors involved in regulatory volume decrease and their roles in modulating outflow facility. METHODS: Primary cultures of bovine TM cells were used. K(+) and Cl(-) currents were studied with whole-cell patch clamping. Swelling was induced by hypotonic shock. [Ca(2+)](i) was measured in TM cells loaded with fura-2. Bovine anterior segments were perfused at constant pressure to measure outflow facility. RESULTS: Hypotonic media activated both the high-conductance Ca(2+)-activated K(+) channel (BK(Ca)) and swelling-activated Cl(-) channel (Cl(swell)) currents and induced release of adenosine 5'-triphosphate (ATP) from TM cells. ATP activated P2Y(2) receptors with the following profile: ATP = uridine 5'-triphosphate (UTP) > adenosine 5'-O-(3-thiotriphosphate) (ATP-gamma S) > adenosine 5'-diphosphate (ADP) = uridine 5'-diphosphate (UDP), and increased BK(Ca) current. Hypotonic medium initially decreased outflow facility in perfused anterior segments, which recovered with time to baseline levels. Addition of tamoxifen or iberiotoxin (Cl(swell) and BK(Ca) blockers, respectively) lengthened the recovery phase, which implies that these channels participate in cell volume regulation. In contrast, an activator of BK(Ca)s (NS1619) produced the opposite effect. CONCLUSIONS: Cell swelling activates a regulatory volume decrease mechanism that implies activation of K(+) and Cl(-) currents and participation of P2Y(2) receptors. Because previous studies have shown that intracellular volume of TM cells is an important determinant of outflow facility, it seems feasible that cell volume regulation would be part of the homeostatic mechanisms of the TM, to regulate the outflow pathway.

Adenosine Triphosphate↗

PubMed2002

Effects of spatial attention on detection and identification of oriented lines.

In this paper, we study the effects of spatial attention on detection and identification of oriented lines presented at near-threshold luminance. In the first experiment, we found that the cuing effect was greater when observers had to discriminate between two close orientations than when they had to discriminate between two far-apart orientations. In the second experiment, we examined the effects of peripheral cues on summation of low-contrast oriented lines. We found that the range of orientations within which summation occurred was greater when the cues were invalid than when they were valid. Our results suggest that attention to a specific location in the visual field modulates the neural channels which code orientation in at least two different ways: (a) spatial attention increases the responsivity of these channels to stimuli presented at this location, and (b) it reduces the bandwidths or ranges of orientations to which these channels are sensitive. These results suggest that the properties of the orientation-tuned channels, including those that seem to exert their effects at early stages of orientation processing (e.g., tuning function), may not be fixed, but rather vary according to the attention being paid to the spatial region within which the target stimulus is presented.

Adult↗