Biomedical subjects

John Christie

Publications and source records attributed to John Christie.

5 recordsLinked to original sources

PubMed2006

Familiarity seekers are fast and novelty seekers are slow.

Christie and Klein (1995) demonstrated that a familiar item (word) rapidly attracts attention when presented simultaneously with an unfamiliar item (nonword). However, this finding has never been replicated. The current study is an attempt at such a replication. Participants were presented a familiar word and unfamiliar nonword in the experimental condition. At varying times after stimulus onset one of the items moved, and the participant reported the direction of the movement. A replication of Christie and Klein would be obtained if performance was better for movement discrimination of the familiar item shortly after onset but not at later intervals. The original finding was replicated in fast participants while slower participants show a different effect. A potential individual difference variable is suggested to explain this difference between the fast and slow participants.

Attention↗

PubMed2005

Phototropin from Chlamydomonas reinhardtii is functional in Arabidopsis thaliana.

Phototropin, a plant blue light photoreceptor, mediates important blue light responses such as phototropism, chloroplast positioning and stomatal opening in higher plants. In Arabidopsis thaliana, two phototoropins, phototropin 1 and 2, are known. Recently, in the unicellular green alga, Chlamydomonas reinhardtii, a phototropin homolog was identified. It exhibits photochemical properties similar to those of higher plant phototropins and is involved in multiple steps of the sexual life cycle of Chlamydomonas. Here, we expressed Chlamydomonas phototropin in Arabidopsis to examine whether it is active in a distantly related plant species. The Arabidopsis mutant deficient in both phototropin 1 and 2 was transformed with a vector containing Chlamydomonas phototropin cDNA fused to a cauliflower mosaic virus 35S promoter. The resulting lines were classified into high, medium and low expressers based on RNA gel blot and immunoblot analyses. Typical phototropin responses were restored in high expression lines. These results demonstrate that Chlamydomonas phototropin is functional in higher plants. Hence, the basic mechanism of phototropin action is highly conserved, even though its apparent physiological functions are quite diverse.

Animals↗

PubMed2005

Does attention cause illusory line motion?

Illusory line motion (ILM) has been shown to occur when a line is presented with one end next to a previously stimulated location. The line appears to be drawn away from the site of stimulation. It has been suggested that this is because of the allocation of attention to the stimulated site. Using an endogenous attentional manipulation (a central arrow cue) with no differences in the display between the two ends of the line at the time of line presentation or immediately prior, no ILM was detected, though there was a small effect in the opposite direction. Those who have found endogenously induced ILM have used an endogenous cue based on a property of a location marker that indicated the cued location. Changing the method of cuing to one based on a property of a peripheral marker instead of a central arrow produced a small but significant report of ILM. The small magnitude of the effect, participant self-reports, and the absence of the effect in the purely endogenous condition, suggest that this was merely a bias. ILM is not generated by endogenous attention shifts.

Attention↗

PubMed2005

Vector averaging of inhibition of return.

Observers detected targets presented 400 msec after a display containing one cue or two to four cues displayed simultaneously in randomly selected locations on a virtual circle around fixation. The cue arrangement was completely uninformative about the upcoming target's location, and eye position was monitored to ensure that the participants maintained fixation between the cue and their manual detection response. Reflecting inhibition of return (IOR), there was a gradient of performance following single cues, with reaction time decreasing monotonically as the target's angular distance from the cued direction increased. An equivalent gradient of IOR was found following multiple cues whose center of gravity fell outside the parafoveal region and, thus, whose net vector would activate an orienting response. Moreover, on these trials, whether or not the targeted location had been stimulated by a cue had little effect on this gradient. Finally, when the array of cues was balanced so that its center of gravity was at fixation, there was no IOR. These findings, which suggest that IOR is an aftermath of orienting elicited by the cue, are compatible with population coding of the entire cue (as a grouped array for multiple cues) as the generator of IOR.

Cues↗

PubMed2002

Using illusory line motion to differentiate misrepresentation (Stalinesque) and misremembering (Orwellian) accounts of consciousness.

It has been suggested that the difference between misremembering (Orwellian) and misrepresentation (Stalinesque) models of consciousness cannot be differentiated (Dennett, 1991). According to an Orwellian account a briefly presented stimulus is seen and then forgotten, whereas by a Stalinesque account it is never seen. At the same time, Dennett suggested a method for assessing whether an individual is conscious of something. An experiment was conducted which used the suggested method for assessing consciousness to look at Stalinesque and Orwellian distinctions. A visual illusion, illusory line motion, was presented and participants were requested to make judgments that reflected what they were aware of. The participants were able to make responses indicating that they were aware of the actual stimulus in some conditions, but only of the illusion in others. This finding supports a claim that the difference between the Orwellian and Stalinesque accounts may be empirically observable and that both types of events may occur depending on task and stimulus parameters.

Consciousness↗