Biomedical subjects

Kestutis Kveraga

Publications and source records attributed to Kestutis Kveraga.

5 recordsLinked to original sources

PubMed2006

Directional uncertainty in visually guided pointing.

Studies of the relationship between stimulus-response uncertainty and reaction times indicate three qualitatively different functions: Hick's law, simple-choice step function, or flat curve (no effect at all). The extent of stimulus-response S-R) compatibility appears to interact with the effects of uncertainty on response times. One possible hypothesis regarding these various S-R uncertainty functions is that uncertainty will have an effect whenever the stimuli and their associated responses are not within the same egocentric spatial coordinates. We tested this hypothesis in 5 undergraduate participants (2 men, M age 18.7 yr., range 18-20) by investigating the time-course of pointing to peripherally located visual targets under four different levels of uncertainty (1, 2, 4, or 8 possible locations). Surprisingly, the resulting response function does not match any of those previously reported. Visually guided pointing produced a quadratic reaction time function as S-R uncertainty increases in log2 steps from 1 to 8.

Adolescent↗

PubMed2005

Effects of stimulus-response uncertainty on saccades to near-threshold targets.

Kveraga et al. (2002, Exp Brain Res 146(3):307-14) reported that saccade latencies are immune to the effects of stimulus-response uncertainty and constitute one of the few response systems that violate Hick's law. Similar effects have been reported for keypresses triggered by vibrations of the fingertips, but robust uncertainty effects were subsequently revealed using weak, low-frequency vibrations (Ten Hoopen et al. 1982, Acta Psychol 50:143-157). We wondered whether immunity of saccadic responses would demonstrate a similar intensity-dependency and therefore re-examined the effects of response entropy on saccade latencies using near-threshold visual stimuli. Saccadic latencies remained independent of stimulus-response uncertainty, indicating that saccadic motor programming is unaffected by the duration of the target detection process.

Adult↗

PubMed2005

Effects of directional uncertainty on visually-guided joystick pointing.

Reaction times generally follow the predictions of Hick's law as stimulus-response uncertainty increases, although notable exceptions include the oculomotor system. Saccadic and smooth pursuit eye movement reaction times are independent of stimulus-response uncertainty. Previous research showed that joystick pointing to targets, a motor analog of saccadic eye movements, is only modestly affected by increased stimulus-response uncertainty; however, a no-uncertainty condition (simple reaction time to 1 possible target) was not included. Here, we re-evaluate manual joystick pointing including a no-uncertainty condition. Analysis indicated simple joystick pointing reaction times were significantly faster than choice reaction times. Choice reaction times (2, 4, or 8 possible target locations) only slightly increased as the number of possible targets increased. These data suggest that, as with joystick tracking (a motor analog of smooth pursuit eye movements), joystick pointing is more closely approximated by a simple/choice step function than the log function predicted by Hick's law.

Adult↗

PubMed2004

Smooth pursuit under stimulus-response uncertainty.

Simple reaction times (RTs) are typically faster than choice reaction times and increase with uncertainty according to Hick's law. Here we show that smooth pursuit eye movement RTs show no effect of SR uncertainty while joystick tracking shows a step change between SRT and CRT, but no significant increases beyond two choices. The results suggest there is a benefit to pre-programming joystick tracking but not for smooth pursuit eye movements (SPEMs).

Adult↗

PubMed2002

Saccades operate in violation of Hick's law.

Hick's law states that response times (RTs) increase in proportion to the logarithm of the number of potential stimulus-response (S-R) alternatives. We hypothesized that time-consuming processes associated with response selection contribute significantly to this effect. We also hypothesized that the latency of saccades might not conform to Hick's law since visually guided saccades can be automatically selected using topographically organized pathways that convert spatially coded visual activity into spatially coded motor commands. We evaluated these hypotheses by examining three response modalities for their compliance with Hick's law: saccades directed to a visual target (prosaccades), saccades directed away from the target (antisaccades) and manual responses in which each digit was associated with a specific target location (key-press responses). Both antisaccades and key-press responses conformed to Hick's law but saccade latencies were completely unaffected by S-R uncertainty. The significance of these findings is considered in terms of the processes of response selection and premotor programming.

Humans↗