Manual tracing efficiency contingent upon stimulus shape and performance practice.

Tracing movements (hand-following the stationary contours of three two-dimensional figures: square, triangle and circle by means of a computer mouse-operated lightspot) were analyzed during five consecutive days. All three figures consisting of four (square, circle) or three (triangle) segments had the same circumference. Three parameters were chosen to express the tracing efficiency: average error, average time and performance quotient (average error per time unit) either for individual segments or the whole figures. The performance quotient was the best for the square and the worst for the circle, yielding better values for horizontal (than for others) segment orientation for the square and triangle. On the contrary, vertical segment orientation was found to be the best for the circle. The performance quotient and average error yielded better values in triangle segments when the right hand was used (all subjects were right-handed). However, considering the whole figures all three parameters displayed better values for the right hand. No differences were found with respect to the direction of tracing movements (clockwise or counter-clockwise). During the first three days both average error and time decreased, the change in later performance is caused by shortening of the average time only.

Changing difficulty level in a one-dimensional tracking task and corresponding heart rate changes.

Subjects were required to track a target consisting of two vertical bars moving with either a constant or a sinusoidally modulated speed across an oscilloscope screen with a joystick-controlled light-spot. Either target size (distance between bars-size guided tasks) or velocity of the target movement (velocity guided tasks), varied throughout different tasks determined by subject's performance. The target's initial movement period was either 2 or 3 seconds. The following parameters were studied: time on-target intervals, time off-target intervals, number of tracking errors, heart rate and tracking error incidence over the cardiac cycle. Time on-target intervals were longer for the velocity guided tasks than for the size guided ones. The same was true for time off-target intervals. Values for both types of intervals decreased gradually over the fixed sequence of tasks for velocity but not for size guided tasks. Heart rate was higher in the size guided task. Tracking error incidence did not depend on the phase of cardiac cycle.

A computerized modification of Sternberg memory test with additional perceptual distraction.

We describe a package of programs in Turbo Pascal which enables us to present six different versions of the modified Sternberg memory test and to evaluate the subject's performance. The program starts presenting a brief series of randomly generated visual stimuli (digits/colors) which are to be memorized, followed by the target stimulus. The series could either include the target or not. Noise in the form of colors or digits could be added to the stimuli. The reaction times of 'yes' or 'no' responses are evaluated separately and presented in numerical and graphic forms.

EEG changes related to one-dimensional hand-tracking.

Central and occipital EEGs were recorded during one-dimensional eye-hand tracking in humans. A negative slow potential shift followed the commitment of tracking errors at electrode O1 and their correction both at O1 and C3. Error commitments were also followed by a relative decrease in alpha and beta-band power at O1, whereas their corrections followed a decrease in beta-band power at O2 and C3.

Selective directional sensitivity in visual motion perception.

We present two experiments demonstrating that: (i) the latency of perception of the position of a small visual target moving towards the fovea is shorter than that of the same target moving away from the fovea; (ii) the reaction time (RT) to onset of motion of the same type of target is also shorter when it moves towards the fovea; and (iii) the RT to onset of motion away from the fovea may be shorter when larger, textured stimuli are employed. The relation of the findings to the existence of two systems for visual motion information processing and to recent neurophysiological findings is discussed.

Cardiac frequency, phase and errors in one-dimensional sensorimotor tracking.

One dimensional manual tracking was investigated in relation to actual heart rate and phase of cardiac cycle. Higher heart rate was combined with increased tracking error incidence and decreased successful tracking time (light spot inside target). Error incidence was time-locked with respect to the phase of cardiac cycle.

Visual perception: double pulse temporal resolution. (Lack of contingency upon the phase of resting cardiac and respiratory cycle).

Double light pulse resolution required longer inter-pulse time intervals of short duration of the pulse. The threshold of double pulse discrimination was not contingent upon the actual phase of cardiac or respiratory cycle.

Estimating the duration of gratings under masking and nonmasking conditions.

Previous research has shown that the subjective duration of very short time intervals decreases with the increase of spatial frequency (SF) and this effect is supposed to be mediated by an early peripheral component of the persistence process called "retinal persistence". As the retinal components of persistence are very likely to be erased by a mask, we suggest that if retinal persistence underlies SF influence on duration estimation, the introduction of a mask would make subjective duration independent of SF. This inference was tested estimating the duration of presentation of square-wave gratings of equal mean luminance and contrast (85%) and of varying SF under two conditions: with and without a mask. Subjective duration decreased with the increase of SF under both experimental conditions It was concluded that retinal persistence does not underlie the SF effect on brief duration perception. Rather, the apparent contrast of the gratings covarying with SF could account for SF influence on perceived duration.

Upright faces seem to have longer duration of presentation than inverted ones.

Nontemporal variables were shown to influence subjective duration. Some of these variables are known to alter recognition performance. We suggested that the ease of pattern recognition underlies the effect exerted by some nontemporal stimuli characteristics on brief duration estimation. In order to test this assumption, recognition was manipulated by presenting facial stimuli in upright and inverted position. Upright faces are known to be recognized easier than inverted ones. The results showed that the upright faces were judged to last longer than the invprted ones when presented for the same time intervals within the range of 10 to 70 ms. It was concluded that recognition performance might play an essential role in the effect of some nontemporal variables on brief duration perception.