Electroretinographically determined spectral sensitivity in the tawny owl (Strix aluco).

The electroretinographic (ERG) responses to single light flashes and to flickering lights were obtained in the tawny owl (Strix aluco). The waveform of the single-flash responses indicated that the owl possesses a duplex retina. Spectral sensitivity was determined with light flickering at a 6 and 25 Hz. The sensitivity curve obtained from the 6-Hz responses has a broad maximum between 500 and 525 nm. The 25-Hz sensitivity curve is narrow with a peak at about 600 nm. The sensitivity curves are compared with behaviorally measured sensitivity curves of the pigeon. A close agreement is found between 25-Hz curve and the pigeon red modulator.     

Deterministic variability and stability in detuned bimanual rhythmic coordination

We examined the effects of crossing different degrees of cooperation and competition on inphase and antiphase 1:1 frequency locked coordination of left- and right-hand-oscillated pendulums. Degree of cooperation was manipulated through the joint frequency of oscillation specified by a metronome (the higher the frequency, the weaker the cooperation), and degree of competition by length (and, therefore, preferred frequency) differences between the two pendulums (the greater the difference, the stronger the competition). Increasing competition was accompanied by either decreasing cooperation (for six participants) or increasing cooperation (for six different participants). On each trial, a participant attempted to produce a steady-state phase relation phi for a given combination of competition and cooperation. Numerical simulations of the extended Haken-Kelso-Bunz (HKB) equation were used to predict (a) the patterns of shift in phi from either 0 or pi radians due to the different competition-cooperation relations and (b) the patterns of variability in phi. It was expected that the HKB equation would be successful in respect to (a), which it was, but not in respect to (b). The observed failure to confirm (b) was expected from the variability due to the different nonharmonic dynamics of the component oscillators, a source of variability not included in the HKB equation. The experimental results together with simulations and analyses of the phase-plane trajectories of the component oscillators suggest the operation of deterministic in addition to stochastic variability in the phase relation of contralateral limbs.     

Brightness enhancement and the Talbot level in stationary gratings

At low spatial frequencies, the perceived brightness of the light phase of a stationary square-wave grating is greater than the brightness of a solid field of equal physical luminance. That increase in the perceived brightness of a grating at low spatial frequencies is analogous to the brightness enhancement observed in a flickering light at low temporal frequencies. At or above the critical spatial frequency—the visual resolution threshold—the brightness of a grating is determined by its space-average luminance, just as the brightness of a flickering light at or above the critical flicker frequency is determined by its time-average luminance in accordance with Talbot’s law. Thus, Talbot’s law applies in the spatial as well as the temporal domain. The present study adds to the evidence that temporal and spatial frequency play analogous roles in some aspects of brightness vision.     

Icon flickering, flicker rate, and color combinations of an icon's symbol/background in visual search performance

The effects of color combinations of an icon's symbol/background and components of flicker and flicker rate on visual search performance on a liquid crystal display screen were investigated with 39 subjects who searched for a target icon in a circular stimulus array (diameter = 20 cm) including one target and 19 distractors. Analysis showed that the icon's symbol/background color significantly affected search time. The search times for icons with black/red and white/blue were significantly shorter than for white/yellow, black/yellow, and black/blue. Flickering of different components of the icon significantly affected the search time. Search time for an icon's border flickering was shorter than for an icon symbol flickering; search for flicker rates of 3 and 5 Hz was shorter than that for 1 Hz. For icon's symbol/background color combinations, search error rate for black/blue was greater than for black/red and white/blue combinations, and the error rate for an icon's border flickering was lower than for an icon's symbol flickering. Interactions affected search time and error rate. Results are applicable to design of graphic user interfaces.     

Preference for tones as a function of frequency (hertz) and intensity (decibels)

An extension of the Wundt hypothesis concerning stimulus intensity and hedonic tone leads to the prediction that Ss prefer tones of intermediate frequency (hertz) and of intermediate intensity (decibels). In Experiment 1, tones varying from 60 to 5000 Hz were presented in a paired comparison procedure, and, as predicted, Ss′ preference was an inverted-U-shaped function of frequency, with the most preferred tones in the range of 400–750 Hz. In Experiment 2, tones varying in intensity from 40 to 90 dB were also presented in a paired comparison procedure, and again the predicted inverted-U-shaped preference function was found, with 50 dB as the preferred intensity. Related research and some unexpected findings are discussed.     

Perception of successive targets presented in invariant-item streams

When two successive, spatially overlapping, targets (S1 and S2) are presented on a blank background, S2 typically dominates in explicit perception. We tested whether S2 dominance is also found for the conditions of presenting S1 and S2 in a stream of irrelevant objects. Successive target letters were presented within a stream of invariant stimulus items (capital Is). The stream items were presented either as a perceptually continuous object where both type and token appeared invariant (60-Hz stream) or as a flickering stream of successive replicas of the invariant stationary object where the type appeared invariant but the token appearance seemed intermittent (20-Hz condition). Compared to the control condition where targets were presented on a blank background we found that (1) recognition rate was lower for targets embedded in a perceptually continuous type-and-token object (60 Hz), but was unchanged for targets in a perceptually flickering sequence of the invariant-object tokens (20 Hz); (2) S1 recognition rate was higher compared to S2 recognition rate within the first epoch of stream (0-150 ms) while within the later stream-epochs S2 dominated over S1 as usual; (3) the overall difference in recognition rates between S1 and S2 was decreased. The results are discussed in the theoretical context of visual masking and attentional blink.     

Flirting with virtual reality

Psychoanalysis encourages patients to experience a virtual reality of the psychoanalytic relationship, in which both image and wish can be experimented with. Originally, the patient's awareness was supposed to move back and forth between the virtual and the actual, in a flickering and uncertain fashion. That is uncomfortable, and analysts have often preferred the domain of virtuality or of actuality, or have denied the distinction altogether. Recent philosophical developments and doubts about transference neurosis and reconstruction further tempt analysts to relax the flickering uncertainty of virtual and actual. Patient and analyst may gain comfort but lose something in the process.     

Context-dependent olfactory learning monitored by activities of salivary neurons in cockroaches

Context-dependent discrimination learning, a sophisticated form of nonelemental associative learning, has been found in many animals, including insects. The major purpose of this research is to establish a method for monitoring this form of nonelemental learning in rigidly restrained insects for investigation of underlying neural mechanisms. We report context-dependent olfactory learning (occasion-setting problem solving) of salivation, which can be monitored as activity changes of salivary neurons in immobilized cockroaches, Periplaneta americana. A group of cockroaches was trained to associate peppermint odor (conditioned stimulus, CS) with sucrose solution reward (unconditioned stimulus, US) while vanilla odor was presented alone without pairing with the US under a flickering light condition (1.0 Hz) and also trained to associate vanilla odor with sucrose reward while peppermint odor was presented alone under a steady light condition. After training, the responses of salivary neurons to the rewarded peppermint odor were significantly greater than those to the unrewarded vanilla odor under steady illumination and those to the rewarded vanilla odor was significantly greater than those to the unrewarded peppermint odor in the presence of flickering light. Similar context-dependent responses were observed in another group of cockroaches trained with the opposite stimulus arrangement. This study demonstrates context-dependent olfactory learning of salivation for the first time in any vertebrate and invertebrate species, which can be monitored by activity changes of salivary neurons in restrained cockroaches.     

A new visual illusion: flickering fields are localized in a depth plane behind nonflickering fields

Flickering regions of the visual field are perceived to lie well behind regions which are not flickered. The depth segregation is not due to luminance differences since the average temporal luminance across all the regions was equal. This depth effect produced by flicker is not dependent on the texture of the visual field; nor does it depend on a specific configuration of the flickering and nonflickering areas. It is optimal at a temporal frequency around 6 Hz, which suggests that visual channels responding maximally to high temporal frequencies are involved in the segregation of perceptual regions in depth.     

Feedback frequency of graphical countdown timers affects pedestrian estimated waiting time at red lights

Graphical countdown timers (similar to a progress bar) have the potential to shorten pedestrians’ perceived waiting time at the red light. Based on the findings from human-computer interaction (HCI) and time estimation theories, the potential may be affected by feedback frequency. This study tested how the feedback frequency of countdown progress bar in traffic light influenced time estimation in a field experiment, and further explored its mechanism in a laboratory experiment. In both experiments, participants estimated various durations (30 s, 45 s, 60 s) under three levels of feedback frequency: low (0.5 Hz), medium (1 Hz), and high (2 Hz). The results showed that although waiting time was underestimated in all conditions, lower feedback frequency led to shorter estimated duration, with slight changes in different contexts. In the traffic context, the effect of feedback frequency was comparable across different countdown duration, but it became stronger at longer countdown duration in the non-traffic context. Overall, the effect of feedback frequency was accompanied by changes in neither arousal level (measured by the subjective scale and physiological indices) nor internal clock speed, which are two critical determinants of time perception. The findings have practical implications on the display design of red light and theoretical implications on time estimation processes.     

Attention-capturing properties of high frequency luminance flicker: Implications for brake light conspicuity

In two experiments, the authors studied the effect of high frequency luminance flicker on reaction time in a simulated driving task. In Experiment 1, 24 research participants performing a primary simulated driving task were required to apply the brake pedal as quickly as possible following the activation of a red light somewhere in their field of vision. The red lights were displayed in one of two ways, (a) with 20 Hz luminance flicker and (b) continuous (no flicker), and presented at three eccentricities, 10°, 45° and 80°. Results showed that the light with 20 Hz flicker was more attention-capturing than the continuous light, but that the effect of 20 Hz flicker on reaction time was not influenced by eccentricity of presentation. The second experiment was identical to the first except that the primary simulated driving task was considerably more attention demanding. Under this higher workload, the light with 20 Hz flicker again proved to be more attention-capturing than the continuous light, and to a greater extent than in Experiment 1. In Experiment 2, there also appeared to be tendency for the light with 20 Hz flicker to be more effective at greater eccentricities. Implications for brake light conspicuity and rear-end collision avoidance are discussed.     

Temporal and spatial factors in the fading of diffuse visual images

Pattern vision breaks down after a period of inspecting a diffusely contoured dark figure upon a ground of uniform brightness and texture. When the field is illuminated with flickering light it is found that the persistence of pattern vision is inversely related to flicker frequency up to the region of fusion. At low flicker frequencies complex figures persist longer than less complex ones of equivalent area, but the reverse applies at frequencies above fusion. These findings are consistent with data obtained from experiments using stabilized retinal images     

Influence of flicker on perceived size and depth

Previous research (e.g., Wong & Weisstein, 1984a, 1985) has shown that flickering stimuli appear to be more distant than nonflickering stimuli at the same physical distance. Given this relation between flicker and perceived depth, inappropriate constancy scaling theories predict that flickering stimuli should be perceived as larger than nonflickering ones. In contrast, links between flicker and motion perception suggest that flickering stimuli should be perceived as smaller than nonflickering ones. Two experiments tested these contrasting predictions. In Experiment 1, 22 subjects compared flickering and nonflickering vertical lines and reported that the flickering stimulus appeared significantly smaller than the nonflickering one. In Experiment 2, 21 subjects reported that the stimuli used in Experiment 1 produced depth effects similar to those reported in previous experiments: flickering stimuli were perceived as more distant than nonflickering ones. The observed effect of flicker on perceived size was contrary to predictions from inappropriate constancy scaling theory, but consistent with views that motion and flicker are processed by the same pathway.     

Choral reading with filtered speech: effect on stuttering

This study investigated use of choral reading with filtered components of speech and whispered speech on the frequency of stuttering. Three passages read by a normal adult male were lowpass filtered with kneepoint frequencies at 100 Hz (approximate glottal source), 500 Hz (source and first formant), and 1 kHz (source and the first two formants). Along with a whispered passage, a normal passage, and a control condition, these stimuli were used in a repeated-measures design with 12 adult stutterers as they read passages while listening to one of the stimuli. Frequencies of stuttering in each condition were analyzed. The choral speech, the 500-Hz, the 1-kHz, and the whispered speech conditions all decreased the frequency of stuttering while the 100-Hz stimuli did not. It is suggested that articulatory events, chiefly the encoded speech output from the vocal tract, create effective cues and may induce fluent speech in people who stutter.     

Antiphase flicker induces depth segregation

We examined the influence of the temporal phase of flickering stimuli on perceptual organization. When two regions of a uniform random-dot field are flickered in temporal alternation with the same flicker rate, one of the regions appears to lie in front of the other. Within the range of temporal frequencies used in the present experiments, depth perception was maximal between 5 and 31.3 Hz. Which region of the two is perceived as lying in front is different from person to person and sometimes fluctuates within the same subject, but when two regions are of different sizes, the smaller region tends to be perceived in front for longer than the larger region. The depth segregation was not due to a luminance difference, because the average temporal luminance of the regions was kept equal. Strikingly, the illusory depth segregation is perceived even between two adjacent regions whose densities of dots, sizes, shapes, and flicker rates are identical. This result suggests that a difference of temporal phase between two flickering regions is crucial for this new depth perception.     

Uniform-field flicker masking in control and specifically-disabled readers

Possible transient-system deficiencies in subjects with specific reading disabilities (SRDs) were investigated in groups of 13-year-old SRDs and control normal readers. In experiment 1, in which a 6 Hz uniform-field flicker (UFF) mask and a stationary test stimulus were used, it was found that the overall effect of UFF masking was to reduce differences in contrast sensitivity between SRDs and normal readers. In experiments 2a and 2b, with UFF masks of 6 and 20 Hz and a 6 Hz moving (experiment 2a) or flickering (experiment 2b) test stimulus, contrast sensitivity in both groups was decreased in the presence of the 6 Hz UFF mask. Only the control group, however, showed a further decrease in sensitivity with the 20 Hz UFF mask. This indicates that the groups differ in terms of a mechanism sensitive to high temporal frequencies. A 20 Hz counterphase flickering test stimulus was used in experiment 3 in the presence of 6 Hz UFF, and it was found that SRDs are less sensitive than controls to 20 Hz flicker across all spatial frequencies used. The 6 Hz mask, however, did not differentially affect the two groups. These findings provide further evidence for a transient-system deficit in the visual systems of SRDs, but also suggest a more complex situation by showing that the two groups differ in a high-temporal-frequency mechanism.     

The dynamics of operations in visual memory: a review and new evidence for oscillatory priming

Evidence from neurophysiological studies indicates that the synchronization of distributed neuronal assemblies in the gamma frequency range is responsible for the integration of discrete stimulus components into coherent wholes (e.g., see Singer, 1999 for review). Psychophysical support for this hypothesis has been reported in experiments that demonstrate that the presentation of a synchronous-premask frame within a 40-Hz flickering premask matrix primes the subsequent detection of a target Kanizsa-type square by generation of a 40-Hz prime (Elliott & Müller, 1998). Psychopharmacological and electrophysiological evidence suggests that this priming mechanism is related to activity in interneuronal networks and relies on the combined function of prefrontal and posterior circuits. In addition, psychophysical experiments demonstrate the existence of a prime-specific visual short-term memory that oscillates at 40 Hz and remains functional for up to 300 ms post-stimulus offset. These results are consistent with a view of the prime as a form of oscillatory mechanism, related to the persistence of visual information (Coltheart, 1980) and in the capacity guided by (prefrontal) top-down influences upon visual-cortical function.     

Visualizing the perisaccadic shift of spatiotopic coordinates

A point light source flickering on and off during a horizontal saccade projects a horizontal array onto the retina. The apparent visual direction of the tail end of the perceived (phantom) array reflects the amount of perisaccadic shift of spatiotopic coordinates that has been completed by the end of the saccade. Four men, saccading 8° to the right across a flashing light, judged the horizontal visual direction of the left (tail) end of the phantom array relative to the left end of a standard 8° array that had projected an image onto the retina before the saccade began. On average, the left ends appeared to be aligned when the last flash in the phantom array was imaged on the retina 7.4° to the right of the image of the left end of the standard array. This result implies that the shift of spatiotopic coordinates is virtually complete by the end of the saccade.     

Temporal characteristics in apparent movement: Omega movement vs. PHI movement

A vertical line stimulus was presented alternately at two positions on an oscillo scope face, with no interstimulus interval. Observation of this stimulus produced haphazard alternation between a number of movement percepts, which were divided into four categories: phi, omega and partial movement, and no movement. Attention to one category did not increase the proportion of time movement in that category it was reported. Proportion of time reported for each category varied differentially as a function of alternation frequency. Upper and lower displacement amplitude limits were measured as a function of frequency for phi and omega movement. Both limits for omega movement differed from those for phi movement. The results imply that phi and omega movement involve separate processing stages in the visual system.     

Evaluation of human consciousness level by means of “automated fluctuation analysis” of high frequency electroencephalogram fitted by double Lorentzians

Since Berger’s discovery of the electroencephalogram (EEG), its analysis has been generally restricted to the visual range (upmost 100Hz) and has ignored higher frequency components. One reason should be that there are no reliable methods to distinguish the brain potentials from muscle activity. We have introduced fluctuation analysis, which is popular method especially in the field of basic physiology to clinical electrophysiology. In our previous study, it was declared that power spectral density (PSD) of human high frequency EEG was composed of double Lorentzians and vanished into white level within 1kHz. Then the purpose of this study is to elucidate the “Automated Fluctuation Analysis,” which enables us to evaluate these higher frequency components and its physiological meaning especially focused on conscious level from wakefulness to sleep stage 1. Seventy-four scalp recording EEGs in twenty normal subjects were studied. In short, “Automated Fluctuation Analysis” is made of three steps: amplification of EEG signal, A/D conversion and Fast Fourier Transform by signal processor and extraction of Lorentzian parameters. PSD of high frequency EEG was displayed on log-log graph and the algorithm fit to the following Lorentzian formula were mathematically based on Brown & Dennis. S(f)=S1/ [1+(f/fc₁)²] + S2/ [1+(f/fc₂)²], where S(f) is PSD (μ V²/Hz) at each frequency (f;Hz), S1 and S2 are the plateau level or zero-frequency power of the initial and second Lorentz, and fc₁ and fc₂ are the corner or half-power frequency of the initial and second Lorentz, respectively. As results, during wakefulness the PSD of high frequency EEG activity was composed of double Lorentzian fluctuations and the power distribution of S1 value in topographical display was frontal dominant. This pattern of S1 value disappeared and S2 value became lower during sleepiness and the second Lorentz disappeared during sleep.