The effect of somaesthetic and acoustic stimuli on the threshold of fusion of paired light flashes in human subjects

The threshold of fusion of paired flashes of light was measured by determining the largest interval between two flashes of light at which they were reported as one and not as two flashes. When a weak electric shock to the skin was presented at the same time as the first flash, the threshold was increased compared to the threshold measured when the flashes were unaccompanied by a shock. As the interval between shock and first flash was increased up to 600 millisec, the effect diminished. A similar pattern of results was obtained using a click, instead of a shock as the additional stimulus. The effect on the two-flash threshold of varying click intensity was also studied. No retroactive effects of the shock on the two-flash threshold were observed.     

Estimating middle-wavelength and long-wavelength cone sensitivity with large, long-duration targets and small, brief targets

Incremental threshold versus field-intensity curves (tvi) and spectral sensitivity functions were measured for 500 nm and 667 nm test flashes, either under the standard two-colour threshold conditions of Stiles (target: 1.0 deg, 200 ms)--which are known to favour detection by the chromatically-opponent pathways--or with a smaller (0.1 deg), shorter-duration (10 ms) target--chosen to favour detection by the non-opponent (achromatic) pathway. The data reveal differences between the two conditions: for the small, brief target, the tvi curves were shallower and less dependent upon wavelength, and the spectral sensitivity functions were narrower than for the standard target.     

Binocular summation of equal-energy flashes of unequal duration

To determine if binocular summation occurs when increment flashes are of equal energy (Bloch’s law) but unequal in luminance-duration parameters, three Ss made temporal forced-choice judgments: (1) monocularly, (2) binocularly when the flashes to each eye were identical, (3) binocularly when the flashes to each eye were of equal energy but different in terms of their luminance and duration parameters, and (4) binocularly when flashes to each eye were separated by 100 msec. Binocular detection rates were consistently superior to monocular detection rates. Similarity in performance between Conditions 2 and 3 indicates that the binocular visual system responds only to the total energy of each monocular flash. The data from two Ss reveal that binocular performance was greater than that predicted on the basis of probability summation.     

Visual sensitivity and mindfulness meditation

Practitioners of the mindfulness form of Buddhist meditation were tested for visual sensitivity before and immediately after a 3-mo. retreat during which they practiced mindfulness meditation for 16 hr. each day. A control group composed of the staff at the retreat center was similarly tested. Visual sensitivity was defined in two ways: by a detection threshold based on the duration of simple light flashes and a discrimination threshold based on the interval between successive simple light flashes. All light flashes were presented tachistoscopically and were of fixed luminance. After the retreat, practitioners could detect shorter single-light flashes and required a shorter interval to differentiate between successive flashes correctly. The control group did not change on either measure. Phenomenological reports indicate that mindfulness practice enables practitioners to become aware of some of the usually preattentive processes involved in visual detection. The results support the statements found in Buddhist texts on meditation concerning the changes in perception encountered during the practice of mindfulness.     

The structure of sensory events and the accuracy of time judgments

We investigated how does the structure of empty time intervals influence temporal processing. In experiment 1, the intervals to be discriminated were the silent durations marked by two sensory signals, both lasting 10 or 500 ms; these signals were two identical flashes (intramodal: VV), or one visual flash (V) followed by an auditory tone (A) (intermodal: VA). For the range of duration under investigation (standards = 0.2, 0.6, 1, or 1.4 s), the results indicated that both the marker length and sensory mode influenced discrimination, but no interaction between these variables or between one of these variables and standard duration was significant. In experiment 2, we compared, for each of four marker-type conditions (VV, AA, VA, AV; and standard = 1 s), intervals marked by two 10 ms signals with intervals marked by unequal signal length (markers 1 and 2 lasting 10 and 500 ms, or 500 and 10 ms). As in experiment 1, the results revealed significant marker-mode and marker-length effects, but no significant interaction between these variables. Experiment 3 showed that, for the same conditions as in experiment 2, perceived duration is not influenced by marker length and that the variability of interval reproductions does not depend on the perceived duration of intervals. The results are discussed in the light of a single-clock hypothesis: marker-length and marker-mode effects are presented as being non-temporal sources of variability associated mainly with sensory and memory processes.     

Hemispheric asymmetries for temporal resolution: A signal detection analysis of threshold and bias

Divided visual field techniques were used to investigate hemispheric asymmetries for (a) the threshold of fusion of two flashes of light and (b) the detection of simultaneous versus successive events for a group of normal, right-handed adults. A signal detection analysis revealed a higher level of accuracy for the right visual field-left hemisphere (RVF-LH) relative to the left visual field-right hemisphere (LVF-RH) for both tasks. These results were interpreted in terms of a general left-hemisphere advantage for the discrimination of fine temporal events. The implications of these results for models of temporary asymmetry that describe the left hemisphere's advantage in terms of an exclusive specialization or relative superiority are then discussed.     

Transient spatial attention degrades temporal resolution

To better understand the interplay between the temporal and spatial components of visual perception, we studied the effects of transient spatial attention on temporal resolution. Given that spatial attention sharpens spatial resolution, can it also affect temporal resolution? To assess temporal resolution, we measured the two-flash fusion threshold When two flashes of light are presented successively to the same location, the two-flash fusion threshold is the minimal interval between the flashes at which they are still perceived as two flashes, rather than a single flash. This assessment of temporal resolution was combined with peripheral precuing--a direct manipulation of transient spatial attention. This allowed us to demonstrate, for the first time, that spatial attention can indeed affect temporal resolution. However, in contrast to its effect on spatial resolution, spatial attention degrades temporal resolution. Two attentional mechanisms that could account for both attentional effects--enhanced spatial resolution and reduced temporal resolution--are discussed.     

Multi- and unisensory visual flash illusions

The role of stimulus structure in multisensory and unisensory interactions was examined. When a flash (17 ms) was accompanied by multiple tones (each 7 ms, SOA < or =100 ms) multiple flashes were reported, and this effect has been suggested to reflect the role of stimulus continuity in multisensory interactions. In experiments 1 and 2 we examined if stimulus continuity would affect concurrently presented stimuli. When a relatively longer flash (317 ms) was accompanied by multiple tones (each 7 ms), observers reported perceiving multiple flashes. In experiment 3 we tested whether a flash presented near fixation would induce an illusory flash further in the periphery. One flash (17 ms) presented 5 degrees below fixation was reported as multiple flashes if presented with two flashes (each 17 ms, SOA =100 ms) 2 degrees above fixation. The extent to which these data support a phenomenological continuity principle and whether this principle applies to unisensory perception is discussed.     

The effects of age and intelligence on the dark-interval threshold

The threshold for the detection of the dark interval between two flashes of light (DIT) was investigated for 240 school children aged 6–17. It was found that the threshold showed a linear decline with chronological age. a finding attributed to physiological aging of the visual receptor system producing diminished persistence of the initial stimulus. This finding was counter to the expectation that the DIT would also indicate the growing potency of a higher-order cognitive process (temporal integration of stimulus traces) which would have caused the DIT to rise at some point along the chronological scale.     

The latency of response in relation to Bloch’s law at threshold’

Bloch’s law failed to hold for latencies of response in a threshold experiment where frequencies ofresponse did, nevertheless, obey the law. Dark-adapted Ss were instructed to respond as soon as they detected flashes of various luminances and durations. The frequency of response increased with increases in stimulus energy (luminance times duration); it was constant when energy was constant. The latency of response, measured from stimulus onset. varied inversely with energy; it also varied inversely with the luminance of flashes that were constant in energy. The results were consistent with data from earlier threshold and simple reaction time experiments.     

Simultaneous visual events show a long-range spatial interaction

A stimulus consisting of two brief flashes separated by a short interval appears to flicker, whereas a single brief flash does not. Performance on a task requiring discrimination of double and single stimuli is adversely affected by simultaneous presentation of a second, similar stimulus at a relatively remote position in the visual field. Most errors occur when target and mask follow different time courses, one double and the other single. The results of four experiments studying this interaction are reported. An effect on performance is observed under binocular, monocular, and dichoptic viewing conditions. Performance is affected up to target to mask distances of at least 20 deg of arc. Performance increases as target-to-mask onset asynchrony is increased, reaching asymptote at asynchronies of between 100 and 150 msec. The precise shape of the stimuli does not appear to be important in determining the size of the effect or whether or not an effect occurs. An analogy between this effect and apparent movement is suggested.     

Two types of short-term visual storage

Seven-letter words were flashed repetitively at various durations above and below the recognition threshold for single flashes. One form of a short-term storage effect was studied by measuring the interstimulus interval between flashes at which S reported that the stimulus became phenomenally discontinuous in time. Storage times reached a maximum of about 300 msec in this task. A second form of storage effect was measured by decreasing the interstimulus interval until S could correctly recognize a repeated stimulus whose duration was below the single-flash recognition threshold; this effect extended to 900 msec in some cases. Each of these effects was reliably obtained for both rare and frequent words. Both forms of storage were increased by providing a dark rather than a lighted adapting field between presentations of the test stimulus. Implications for Information processing of brief displays are discussed.     

Assessing the belief bias effect with ROCs: reply to Dube, Rotello, and Heit (2010)

Dube, Rotello, and Heit (2010) argued (a) that the so-called receiver operating characteristic is nonlinear for data on belief bias in syllogistic reasoning; (b) that their data are inconsistent with Klauer, Musch, and Naumer's (see record 2000-02818-008) model of belief bias; (c) that their data are inconsistent with any of the existing accounts of belief bias and only consistent with a theory provided by signal detection theory; and (d) that in fact, belief bias is a response bias effect. In this reply, we present reanalyses of Dube et al.'s data and of old data suggesting (a) that the receiver operating characteristic is linear for binary "valid" versus "invalid" responses, as employed by the bulk of research in this field; (b) that Klauer et al.'s model describes the old data significantly better than does Dube et al.'s model and that it describes Dube et al.'s data somewhat better than does Dube et al.'s model; (c) that Dube et al.'s data are consistent with the account of belief bias by misinterpreted necessity, whereas Dube et al.'s signal detection model does not fit their data; and (d) that belief bias is more than a response bias effect.     

Unconscious perception or not? An evaluation of detection and discrimination as indicators of awareness

Most investigations of unconscious perception use a dissociation design in which an awareness variable (e.g., detection) is compared with a perceptual processing variable (e.g., identification). Unconscious perception is inferred when the awareness variable lacks sensitivity to the stimulus but evidence of perceptual processing is still obtained. In two studies we examined the relationship between word identification and detection (Study 1) or discrimination (words vs. nonwords; Study 2) with a variety of techniques. In both studies, dissociations suggestive of unconscious perception occurred when the data were examined with subjective threshold approaches, but these differences disappeared when the variables were compared with techniques derived from signal detection theory (SDT). These results do not support unconscious perception in subjective threshold paradigms. In addition, detection appears to be the most sensitive and appropriate task for assessing stimulus awareness, provided that several SDT assumptions are met.     

A new EOG-based eyeblink detection algorithm

Accurate and efficient operator functional state classification and assessment based on physiological data have many important applications ranging from operator monitoring to interaction and control of human/machine systems. Eyeblink characteristics are frequently used as physiological indicators for this purpose. In this paper, we describe an efficient and robust eyeblink detection algorithm based on nonlinear analysis of the electrooculogram (EOG) signal. The performance of the algorithm was evaluated via data analysis results of several benchmark test sets in comparison with another eyeblink detection algorithm.     

Suprathreshold binocular interactions for grating patterns

Binocular interactions of suprathreshold grating patterns have been investigated using a reaction time measure of contrast detection. Simple reaction times were determined for monocular and binocular viewing conditions over a contrast range from .63 to near threshold. The results from all subjects showed binocular summation for contrast levels near threshold, but there was considerable variation across subjects for contrast levels above threshold. Some subjects showed summation over the entire contrast range, but other subjects showed either binocular inhibition or binocular facilitation for some range of contrast levels. The pattern of binocular interaction for a given subject was consistent for several spatial frequencies. The differences in types of interaction between subjects, the variation in magnitude of binocular interaction with contrast level for each subject, and the data from experiments involving stimulation of noncorresponding retinal areas show that the binocular interactions found for suprathreshold stimuli cannot be accounted for on the basis of probability, and must, therefore, result from physiological interactions between the two eyes. These interactions have been investigated further under conditions of (1) induced fixation disparity, (2) horizontal gratings, and (3) orthogonally oriented gratings.     

The effect of stimulus amplitude on the threshold of fusion of paired flashes

Four experiments are described in which the threshold of fusion of paired flashes was measured. The intensity of the single flashes making up the pairs was varied independently. The results showed that when the first flash of the pair was the more intense, the threshold of fusion increased linearly as the difference in the log intensity of the two flashes. A proposal put forward to explain the results suggested the “noise” created by the first flash of the pair has to dissipate to a critical extent to allow the “signal” arising from the second flash to be detected.     

Distribution effects of orthographic similarity and priming by masked repetition]

This research centres on the effect that the orthographic neighbourhood has in the visual recognition of words. Specifically, we studied to what extent orthographic neighbourhood distribution, that is, the number of letter positions allowing formation of at least one neighbour (Pugh, Rexer, Peter, & Katz, 1994), influences the masked repetition priming effect. In a previous study (Mathey, Robert, & Zagar, 2004), interaction between neighbourhood distribution and orthographic priming was obtained in the lexical decision task. The Interactive Activation Model (IA; McClelland & Rumelhart, 1981) simulated this interaction. With the orthographic priming effect modified for distribution of the neighbourhood of target words, it was necessary to study whether the repetition priming effect also varied as a function of this indicator. Studying this interaction presents a major theoretical issue in specifying the activating and inhibiting processes presented in the IA model. Simulations were produced to obtain precise model predictions regarding the neighbourhood distribution effect in a repetitive priming situation for our experimental material. Target words all had two neighbours that were most frequent. These neighbours were isolated, that is, distributed over two letter positions (e.g.: TAUX/faux-toux), or associated, i.e., concentrated on one single position (e.g., SEAU/beau-peau). Targets were preceded by an identical priming (repetitive priming; e.g.: seau-SEAU) or by controlled priming (e.g., &-SEAU). The simulation results obtained using the IA model show the facilitating effects of neighbourhood distribution and repetitive priming, but no interaction between these factors. The experimental results obtained in a lexical decision task confirm these predictions. Thus, the empirical data replicate the neighbourhood distribution's facilitating effect (Mathey & Zagar, 2000) as well as the facilitating effect of masked repetition (Forster & Davis, 1984). Finally, the most interesting result is that the facilitating effect of repetition is comparable for target words with associated neighbours and target words with isolated neighbours. An explanation of the combined effects of the orthographic neighbourhood and orthographic masked repetition priming, integrating data from literature as well as from the current study, is proposed within the framework of the IA model.     

Short-term memory for the timing of auditory and visual signals.

Short-term memory for the timing of irregular sequences of signals has been said to be more accurate when the signals are auditory than when they are visual. No support for this contention was obtained when the signals were beeps versus flashes (Experiments 1 and 3) nor when they were sets of spoken versus typewritten digits (Experiments 4 and 5). On the other hand, support was obtained both for beeps versus flashes (Experiments 2 and 5) and for repetitions of a single spoken digit versus repetitions of a single typewritten digit (Experiment 6) when the subjects silently mouthed a nominally irrelevant item during sequence presentation. Also, the timing of sequences of auditory signals, whether verbal (Experiment 7) or nonverbal (Experiments 8 and 9), was more accurately remembered when the signals within each sequence were identical. The findings are considered from a functional perspective.     

The luminance of tachistoscope lamps as a function of flash duration

The steady-state luminance of the lamps in a commonly used Iconix tachistoscope was shown to depend, in a complex nonlinear fashion, upon the length of time the lamps were lit. This was probably due to variations in lamp temperature with time. An integrating photometer was used to measure the light energy present in short flashes and in time periods of various durations with the lamps burning continuously. The equivalent luminance of short flashes was calculated by comparing values obtained by integration over a short flash with values resulting from integration, over an identical duration, of the lamps in a steady-state. With flashes up to 50 msec in nominal duration, luminous energy was less than one-half of that present in the same duration with the lamps burning continuously. The importance of this information for the interpretation of tachistoscopic experiments, as well as possible means of monitoring the effects, are discussed.