Block‐wise conflict adaptation of visual selectivity: Role of hemisphere‐dependent and location‐specific mechanisms

Three experiments investigated views on modulation of visual selectivity that involve hemisphere‐dependence and conflict frequency based views for a whole display. In each experiment, 16 participants completed a flanker task with compatible/incompatible stimulus arrays presented in the left, center, or right visual fields. The relative frequency of the compatible stimulus‐arrays within a trial block was varied as a function of the visual field. In Experiment 1, the relative compatibility frequency in the lateral visual fields was varied (75% / 25%) but not in the center visual field (50%). The results showed that in the lateral visual fields, the performance between the compatible and incompatible trials differed more in conditions with few (vs. many) compatibility trials. Experiments 2 and 3 validated these findings. In Experiment 2, the compatibility frequency varied in the center visual field but not in the lateral fields, resulting in performance effects in all three visual fields. Experiment 3 varied the magnitude of the differences between the compatibility and incompatibility frequencies. Together, the findings showed that participants adjusted to the frequencies of compatible stimuli in all visual fields, indicating conflict adaptation that depends on the relative frequencies of compatible stimuli. The results also suggest that this adaptation is associated with hemisphere‐dependent and location‐specific mechanisms.     

Stimulus disparity and punisher control of human signal-detection performance

The present experiment examined the effects of varying stimulus disparity and relative punisher frequencies on signal detection by humans. Participants were placed into one of two groups. Group 3 participants were presented with 1:3 and 3:1 punisher frequency ratios, while Group 11 participants were presented with 1:11 and 11:1 punisher frequency ratios. For both groups, stimulus disparity was varied across three levels (low, medium, high) for each punisher ratio. In all conditions, correct responses were intermittently reinforced (1:1 reinforcer frequency ratio). Participants were mostly biased away from the more punished alternative, with more extreme response biases found for Group 11 participants compared to Group 3. For both groups, estimates of discriminability increased systematically across the three disparity levels and were unaffected by the punisher ratios. Likewise, estimates of response bias and sensitivity to the punisher ratios were unaffected by changes in discriminability, supporting the assumption of parameter invariance in the Davison and Tustin (1978) model of signal detection. Overall, the present experiment found no relation between stimulus control and punisher control, and provided further evidence for similar but opposite effects of punishers to reinforcers in signal-detection procedures.     

Inhibitory processes in auditory selective attention: Evidence of location-based and frequency-based inhibition of return

The possibility that there is an inhibitory component to auditory covert orienting was addressed. Each trial consisted of a cue followed by a target, and listeners were required to detect, localize, or identify the frequency of the target. At 150-msec stimulus onset asynchrony (SOA), performance was best when stimuli sounded from the same location or were of the same frequency. However, at 750-msec SOA, performance was best when stimuli differed in location or were of different frequencies. These results document the existence of both location-based and frequency-based auditory inhibition of return.     

The role of auditory memory traces in attention to frequency

Three cued signal detection experiments demonstrated a role for auditory memory traces in frequency selectivity. The extent to which the cue predicted the signal frequency affected the size of the advantage for signals at the cue frequency over those at distant frequencies when the cue-signal gap was 10 sec but not when it was 1 sec. Detection of occasional signals presented at uncued frequencies was enhanced when they matched the frequency of cues from recent trials. With "relative" cues, which were usually followed by signals at the musical fifth above the cue frequency, performance on occasional signals at the cue frequency was enhanced relative to other unexpected frequencies. These results suggest that, regardless of the listener's expectations and intentions, the detectability of a signal is enhanced if its frequency matches an existing memory trace. One form of voluntary attention to frequency may involve maintaining traces that would otherwise slowly decay.     

Lateralization of very-short-duration tone pulses of low and high frequencies

The position and image-width of the simultaneous images produced by very short tone pulses were measured as a function of interaural time difference (ITD) at both low- (250 and 800 Hz) and high- (2500 and 8000 Hz) frequencies using a direct-estimation technique.

Primary images are lateralized towards the ear receiving the leading stimulus. At low frequencies image position is proportional to interaural phase-difference (IPD) below 90° and remains at the lead-ear for larger values. At high frequencies image position is proportional to ITD up to 500-1000 μsec. Secondary images are reported on the opposite side of the head for IPDs greater than 180° at low frequencies, and at ITDs greater than 500 μsec at high frequencies. Image width is approximately constant for all ITDs and both images at a given frequency, but becomes more compact as frequency increases.

The data are discussed in terms of onset cues and stimulus fine-structure cues. The best explanation is in terms of an onset mechanism, but one that is calibrated in terms of IPD at low frequencies. The existence of double images is explained in terms of a breakdown in the mechanism determining fusion.     

Interactions among affect, cognition, and visuomotor coordination as measured in words and symbols

The associative frequencies of responses to stimulus words during free and controlled forced-choice word-association tests correlate well with each other and with assessments of the affective character (emotional content) of the stimulus words for the test subjects (Osgood Index) for three samples of volunteer French undergraduate students (ns = 200, 64, and 72). These indices correlate negatively with the subjects' performance on Digit Symbol Substitution tests. Neisser's theory of schemata and Edelman's theory of neuronal group selection may provide insight into this relationship. If the associative frequency of a subject's response decreased, the affective content of the word stimulus (as perceived by the subject) diminished as well. This relationship was associated with a relatively higher score on Digit Symbol Substitution. Conversely, it was observed that subjects whose responses were characterized by high associative frequencies (whether the response was spontaneous or forced-choice) rated the stimulus words as having a relatively stronger affective content or emotional character and performed less well on Digit Symbol Substitution.     

Interpreting the effects of image manipulation on picture perception in pigeons (Columba livia) and humans (Homo sapiens)

The effects of picture manipulations on humans' and pigeons' performance were examined in a go/no-go discrimination of two perceptually similar categories, cat and dog faces. Four types of manipulation were used to modify the images. Mosaicization and scrambling were used to produce degraded versions of the training stimuli, while morphing and cell exchange were used to manipulate the relative contribution of positive and negative training stimuli to test stimuli. Mosaicization mainly removes information at high spatial frequencies, whereas scrambling removes information at low spatial frequencies to a greater degree. Morphing leads to complex transformations of the stimuli that are not concentrated at any particular spatial frequency band. Cell exchange preserves high spatial frequency details, but sometimes moves them into the "wrong" stimulus. The four manipulations also introduce high-frequency noise to differing degrees. Responses to test stimuli indicated that high and low spatial frequency information were both sufficient but not necessary to maintain discrimination performance in both species, but there were also species differences in relative sensitivity to higher and lower spatial frequency information.     

Repeated observation of an uncertain signal

The focus here is on sensory adaptation, or progressively more appropriate attention, as repeated observations yield more information about a signal with an uncertain parameter. The signal was a brief sinusoid; its uncertain parameter was frequency. Detection performance is predicted from data on a signal of known and constant frequency, as a function of the number of frequencies the uncertain signal could assume. A comparison condition presented a signal that varied in a manner not permitting adaptation. Models derived from signal detection theory describe the ideal observation processes for the three signal conditions, and supply quantitative predictions of relative performances. The models are generally supported by the data.     

Magnitude estimation and magnitude production: stimulus frequency effects on magnitudes of lingual vibrotactile sensation

The methods of magnitude estimation and magnitude production were employed to investigate the effects of stimulus frequency on supra-threshold lingual-vibrotactile sensation-magnitude functions. The method of magnitude estimation was used to obtain numerical judgments of sensation magnitudes for nine stimulus intensities presented to the anterior dorsum of the tongue. The vibrotactile stimulus frequencies employed for 10 subjects (M age = 21.1 yr.) were 100, 250, and 400 Hz. The numerical responses obtained during the magnitude-estimation task were in turn used as stimuli to obtain magnitude-production values for the same three vibrotactile stimulus frequencies. The results appeared to present two suggestions. First, the effects of stimulus frequency on lingual vibrotactile-sensation magnitudes may be dependent on the psychophysical method used in any particular experiment. Second, lingual-vibrotactile magnitude-estimation scales may demonstrate asymptotic growth functions above about 25 dB sensation level. The limitation in the growth of sensation magnitude occurred for all three vibrotactile stimulus frequencies employed.     

Identification and bisection of temporal durations and tone frequencies: common models for temporal and nontemporal stimuli

Two experiments examined identification and bisection of tones varying in temporal duration (Experiment 1) or frequency (Experiment 2). Absolute identification of both durations and frequencies was influenced by prior stimuli and by stimulus distribution. Stimulus distribution influenced bisection for both stimulus types consistently, with more positively skewed distributions producing lower bisection points. The effect of distribution was greater when the ratio of the largest to smallest stimulus magnitude was greater. A simple mathematical model, temporal range frequency theory, was applied. It is concluded that (a) similar principles describe identification of temporal durations and other stimulus dimensions and (b) temporal bisection point shifts can be understood in terms of psychophysical principles independently developed in nontemporal domains, such as A. Parducci's (1965) range frequency theory.     

Contours of equal perceived amplitude and equal perceived frequency for electrocutaneous stimuli

Previous measurements of equal-sensation contours for electrocutaneous stimuli consisting of repeated bursts of biphasic pulses have shown that stimulus frequency has little effect on perceived amplitude, and that stimulus amplitude has no effect on perceived frequency. These earlier contours, however, were measured over a very restricted range of amplitude and frequency or for a single perceived amplitude or perceived frequency. Contours of equal perceived amplitude and equal perceived frequency were measured in the present study for stimuli covering most of the useable range of amplitudes and frequencies: 3–12 dB SL and 4–64 Hz. Eight naive subjects generated contours of equal perceived amplitude at four reference amplitudes via Békésy tracking, and 8 additional subjects generated contours of equal perceived frequency at three reference frequencies. The contours of equal perceived amplitude declined slightly but significantly with increases in stimulus frequency, consistent with previous results. The shape of the contours was also slightly dependent on the amplitude of the reference stimulus. Contours of equal perceived frequency were unaffected by stimulus amplitude on the average, but the contour shape did vary modestly, though erratically, with reference frequency.     

Spectral cues which influence monaural Localization in the horizontal plane

An extensive series of behavioral tests was carried out to determine what region, or regions, of the sound spectrum were critical for locating sounds monaurally in the horizontal plane. Seven subjects were requested to locate narrow bands of noise centered at different frequencies, combinations of these noise bands, low-pass, high-pass, and broadband noise. As observed in an earlier study, increasing bandwidth did not necessarily lead to improved localization performance until the band became broad, including, for example, all frequencies above 4.0 kHz. What seems to be happening is that listeners perceive narrow bands of noise originating from restricted places in the horizontal plane which may differ one from another depending on the frequency composition of the stimulus. In several instances, if two noise bands were presented simultaneously, the resulting stimulus was located with reasonable accuracy provided each component, when presented singly, was perceived as emanating from clearly separate azimuthal positions. If, however, two noise bands, which were perceived to originate from approximately the same azimuthal position when presented singly, were now presented simultaneously, the resulting stimulus still was perceived to originate from the same region of the horizontal plane. This, then, is a case where augmenting the spectral content of the stimulus does not bring about improved performance. We suggest that the expression of judgmental biases in the apparent location of a band of noise may prove useful for understanding why some stimuli of specified width and center frequency are localizable while others are not.     

Some effects of methylphenidate on stimulus control of ratio avoidance behavior in the rat

After exposure to an avoidance schedule which included a warning signal, a rat was placed on a multiple schedule in which the first component was the same as before, i.e., a single response reset the response-shock interval, delaying shock, and the second component differed only in that four bar-presses were required to postpone shock. A fixed ratio requirement of four responses (FR 4) generated behavior resembling a fixed ratio requirement of one response (FR 1) since responding was controlled by the warning signal but more shocks were received. At a dosage of 2 mg/kg, methylphenidate given intraperitoneally decreased shock frequency during FR 4 periods while FR 1 behavior was not affected; at 4 mg/kg, stimulus control of avoidance responding was impaired during both components. Results at 4 mg/kg were partially confirmed by two animals exposed to an FR 4 avoidance schedule which included a warning signal but with different parameters. Response distributions showed that methylphenidate increased response rates in the absence of the warning signal, i.e., stimulus control of ratio-avoidance behavior was impaired although the increased response rates reduced shock frequency. One hour later responses again occurred more frequently during the signal than in its absence but shocks were less frequent than during control (non-drug) periods.     

Oculomanual Coordination in Tracking of Pseudorandom Target Motion Stimuli

Oculomanual coordination was investigated in 9 healthy subjects during tracking of pseudorandom motion stimuli. Each subject was required to track visual stimuli under eye-hand (EH) and eye-alone (EA) conditions. Subjects were exposed to 3 types of mixed sinusoidal stimulus with varying frequency or amplitude of the highest frequency component, or various degrees of irregularity. Progressive degradation in tracking performance was nonlinearly induced by an increase in either (a) the highest frequency component or (b) its amplitude, but not by stimulus irregularity. No significant difference was found in eye velocity gain and phase under the EH and EA conditions. Eye and hand responses were found to be highly correlated in gain and phase when compared across frequencies and motion stimuli. The results suggest that frequency and amplitude are dominant factors controlling the breakdown of oculomanual performance in response to pseudorandom stimuli. Frequency responses of smooth pursuit eye movements are not affected by the hand motion in pursuit of unpredictable stimuli. Eye and hand motor systems appear to share common nonlinear drive mechanisms when pursuing pseudorandom target motion stimuli.     

Retinal and extraretinal information in movement perception: how to invert the Filehne illusion

During a pursuit eye movement made in darkness across a small stationary stimulus, the stimulus is perceived as moving in the opposite direction to the eyes. This so-called Filehne illusion is usually explained by assuming that during pursuit eye movements the extraretinal signal (which informs the visual system about eye velocity so that retinal image motion can be interpreted) falls short. A study is reported in which the concept of an extraretinal signal is replaced by the concept of a reference signal, which serves to inform the visual system about the velocity of the retinae in space. Reference signals are evoked in response to eye movements, but also in response to any stimulation that may yield a sensation of self-motion, because during self-motion the retinae also move in space. Optokinetic stimulation should therefore affect reference signal size. To test this prediction the Filehne illusion was investigated with stimuli of different optokinetic potentials. As predicted, with briefly presented stimuli (no optokinetic potential) the usual illusion always occurred. With longer stimulus presentation times the magnitude of the illusion was reduced when the spatial frequency of the stimulus was reduced (increased optokinetic potential). At very low spatial frequencies (strongest optokinetic potential) the illusion was inverted. The significance of the conclusion, that reference signal size increases with increasing optokinetic stimulus potential, is discussed. It appears to explain many visual illusions, such as the movement aftereffect and center-surround induced motion, and it may bridge the gap between direct Gibsonian and indirect inferential theories of motion perception.     

Right or wrong, familiar or novel in pictorial list discrimination learning

The interaction between nonassociative learning (presentation frequencies) and associative learning (reinforcement rates) in stimulus discrimination performance was investigated. Subjects were taught to discriminate lists of visual pattern pairs. When they chose the stimulus designated as right they were symbolically rewarded and when they chose the stimulus designated as wrong they were symbolically penalised. Subjects first learned one list and then another list. For a "right" group the pairs of the second list consisted of right stimuli from the first list and of novel wrong stimuli. For a "wrong" group it was the other way round. The right group transferred some discriminatory performance from the first to the second list while the control and wrong groups initially only performed near chance with the second list. When the first list involved wrong stimuli presented twice as frequently as right stimuli, the wrong group exhibited a better transfer than the right group. In a final experiment subjects learned lists which consisted of frequent right stimuli paired with scarce wrong stimuli and frequent wrong stimuli paired with scarce right stimuli. In later test trials these stimuli were shown in new combinations and additionally combined with novel stimuli. Subjects preferred to choose the most rewarded stimuli and to avoid the most penalised stimuli when the test pairs included at least one frequent stimulus. With scarce/scarce or scarce/novel stimulus combinations they performed less well or even chose randomly. A simple mathematical model that ascribes stimulus choices to a Cartesian combination of stimulus frequency and stimulus value succeeds in matching all these results with satisfactory precision.     

Transfer to intermediate forms following concept discrimination by pigeons: chimeras and morphs

Two experiments examined pigeons' generalization to intermediate forms following training of concept discriminations. In Experiment 1, the training stimuli were sets of images of dogs and cats, and the transfer stimuli were head/body chimeras, which humans tend to categorize more readily in terms of the head part rather than the body part. In Experiment 2, the training stimuli were sets of images of heads of dogs and cats, and the intermediate stimuli were computer-generated morphs. In both experiments, pigeons learned the concept discrimination quickly and generalized with some decrement to novel instances of the categories. In both experiments, transfer tests were carried out with intermediate forms generated from both familiar and novel exemplars of the training sets. In Experiment 1, the pigeons' transfer performance, unlike that of human infants exposed to similar stimuli, was best predicted by the body part of the stimulus when the chimeras were formed from familiar exemplars. Spatial frequency analysis of the stimuli showed that the body parts were richer in high spatial frequencies than the head parts, so these data are consistent with the hypothesis that categorization is more dependent on local stimulus features in pigeons than in humans. There was no corresponding trend when the chimeras were formed from novel exemplars. In Experiment 2, when morphs of training stimuli were used, response rates declined smoothly as the proportion of the morph contributed by the positive stimulus fell, although results with morphs of novel stimuli were again less orderly.     

Discriminated punishment: avoidable and unavoidable shock

Warning stimuli for two punishment conditions were alternated with periods of appetitive responding by rats. In either warning stimulus, the first response produced a brief shock, terminated the stimulus, and started an interval during which the baseline appetitive schedule was in effect. Not responding resulted in stimuli of random duration, which terminated with a shock under one condition and without a shock under the other. Each subject was exposed to several shock intensities, with trials for the two conditions programmed during alternate portions of the session. In general, response frequency in the warning signal for either condition decreased with increasing intensity; however, at a given intensity, responding was more frequent in the stimulus invariably terminating with shock than in the stimulus terminating without shock when no response was made. The frequency difference was greatest at intensities intermediate between those producing minimal and maximal suppression.     

On utrocular discrimination

Observers with good stereoacuity judged which eye received sine-wave grating patterns in a two-category forced-choice procedure. Large individual differences were found, but for most observers reliable discrimination was achieved at low spatial frequencies. No observer could perform the task above chance levels at high spatial frequencies. Discrimination was unaffected by retinal location, grating orientation, grating contrast, stimulus duration, or practice with feedback. Among observers who could perform the task, the following results were obtained: (1) Introduction of high spatial frequency components did not interfere with performance so long as a low spatial frequency component was present. (2) When gratings of low equal spatial frequency were presented to both eyes simultaneously at different contrast levels, observers could identify which eye received the higher contrast. (3) At low spatial frequencies, observers could distinguish monocular from binocular presentation. (4) Temporal frequency variations (counterphase flicker) influenced performance for some observers. Binocular summation and interocular transfer were unaffected by the spatial frequency variations which modulate utrocular discrimination. A new procedure for measuring stereopsis was developed which made possible comparison of utrocular discrimination with stereopsis at specific spatial frequencies. Stereopsis appeared mildly affected by spatial frequency.     

Comparison of child and adult vibrotactile thresholds as a function of frequency and duration

Psychophysical thresholds for the detection of sinusoidal vibration of the thenar eminence of the hand were determined for children and adults. The subjects in the child group were between 8 and 11 years old, and the adults were between 20 and 39 years old. Measurements were made for vibration frequencies ranging from 18 to 700 Hz and stimulus durations ranging from 28 to 1,000 msec. For both children and adults, thresholds were a Il-shaped function of stimulus frequency. However, the exact form of the function was influenced by the age of the subjects. At frequencies above 200 Hz, thresholds were virtually identical for children and adults, but below this frequency children were more sensitive than adults. This finding, in combination with known changes in the anatomy of the Pacinian corpuscle with age, is in agreement with a filter model of this cutaneous receptor. Furthermore, variation of stimulus duration resulted in data in agreement with the theory that two classes of mechanoreceptors, Pacinian and non-Pacinian, mediate the perception of vibration.