Biomedical subjects

E Põder

Publications and source records attributed to E Põder.

4 recordsLinked to original sources

PubMed2001

Change in feature space is not necessary for the flash-lag effect.

To achieve perceptual match between a flashed target and a gradually changing one, the flashed target should have the feature value corresponding to the value to be obtained by the gradually changing target only later. Flashed target should be positioned ahead of the continuously moving one in order to be perceived as aligned (Nijhawan (1994). Nature, 370, 256-257); with continuously changing colour, spatial frequency, pattern entropy or luminance, the flashed target should have feature value which changing target obtains only later (Sheth, Nijhawan, & Shimojo (2000). Nature Neuroscience, 3, 489-495). It was found that flash-lag effect is present even if the continuously accumulating pre- and post-target input consists in spatially and featurally invariant stimulation. The perceptual precedence of the target in stream over its synchronous single-flashed replica may result from perceptual acceleration where newly arriving visual signals are facilitated by the locally preceding stimulation.

Humans↗

PubMed2001

Size-based selection in rapid serial visual presentation.

Several recent studies [Farell, B., & Pelli, D. (1993). Can we attend to large and small at the same time? Vision Research, 33, 2757-72; Shih, S., & Sperling, G. (1996). Is there feature-based attentional selection in visual search? Journal of Experimental Psychology: Human Perception and Performance, 22, 758-79] have found that visual selection based on the size of stimuli is impossible when the stimuli are presented in rapid succession in overlapping positions (RSVP paradigm). In the present study effective size-based selection is demonstrated in several conditions with RSVP stimuli. Attention to specific size is highly efficient when stimuli are presented in a single location (at fixation point) and may be possible also with a few (2-4) locations. When overlapping small and large characters are presented without abrupt onsets, then selection by size is effective at least over six locations. The results are explained by certain mandatory properties of spatial attention.

Adult↗

PubMed1999

Search for feature and for relative position: measurement of capacity limitations.

Palmer and his associates (Palmer, Ames & Lindsey (1993). Journal of Experimental Psychology: Human Perception and Performance, 19, 108-130; Palmer (1994). Vision Research, 34, 1703-1721) have confirmed that searches for simple feature targets are not limited by perceptual processing capacity and the effect of set size on performance can be accounted for by integration stage processes only. In this study I used a similar difference threshold method with target and distractor stimuli defined by the relative position of their elements (line drawings of bisected squares) and found clear capacity limitations. Feature search condition, however, with nearly comparable bisected square stimuli did replicate the results of Palmer and associates. This experiment demonstrates that a search for targets defined by relative position in the set of line drawing type of stimuli is fundamentally different from a search for more simple (feature) stimuli and may conform to a strict capacity limited model.

Adolescent↗

PubMed1998

Speed of elementary visual recognition operations in Parkinson's disease as measured by the mutual masking method.

Pairs of mutually different, spatially overlapping letters were exposed for recognition to groups of patients with Parkinson's disease (PD) and the age-matched control group. Stimulus onset asynchrony (SOA), medical treatment status (de novo vs. treated), and predominant symptoms (tremor vs. hypokinetic rigidity) were an other main variables. The highly significant main effects of SOA and health status demonstrated slowing of elementary visual recognition operations in Parkinson's disease; the results are based on the experimental method that requires neither fast manual responses nor tracking of the display events by saccadic eye movements. Significant interaction between the temporal order of stimulus exposure and health status showed that impairment due to PD was more pronounced for the first stimulus, including the de novo group. Qualitatively similar recognition functions in the binocular and dichoptic conditions showed that the typical pattern of results--prevalence of S2 over S1 at intermediate SOAs--cannot be attributed to retinal processes and should be originating from central processes. An earlier finding (Bachmann, 1994) that PD patients whose nonspecific thalamic nuclei were stimulated intracranially produced qualitatively unusual recognition functions that should have been the result of stimulation, rather than PD as such.

Adult↗