Effects of differences in timbre on sequential grouping

Differences in the timbre of sounds in a sequence can affect their perceptual organization. Using a performance measure, Hartmann and Johnson (1991) concluded that streaming could be predicted primarily by the extent to which sounds were passed by different peripheral channels. However, results from a rating task by Dannenbring and Bregman (1976) suggested that sounds in the same spectral region (passed by the same peripheral channels) can be allocated to different streams. In Experiment 1, it was found, using an interleaved melody task, that target sounds could be selected from distractors in the same spectral region more easily when they differed in timbre. This finding might result from primitive stream segregation or schema-driven selection, but not from peripheral channeling. In Experiment 2, a rhythm discrimination task was used, requiring the sounds to be integrated for good performance. Differences in timbre impaired performance, indicating the occurrence of primitive stream segregation.     

Effects of stimulus probability and visual similarity on stimulus encoding

Visual similarity, stimulus probability, and stimulus contrast were manipulated in two memory-scanning experiments to determine how stimulus probability affects encoding. Two hypotheses were tested: The first, a featural facilitation hypothesis, localizes the effect of stimulus probability on feature extraction; the second claims that stimulus probability has its effect on stimulus recognition. In both experiments, visual similarity was found to slow encoding, particularly under low-contrast conditions. This effect was larger for low probability stimuli than for high probability stimuli and increased as the difference in probability between two visually similar stimuli increased. These results are inconsistent with the featural facilitation hypothesis, but can be explained in terms of differential priming of internal recognition responses for members of the stimulus set, such that more probable members are more easily recognized.     

Integrating sequential arrays in visual short-term memory

Are sequential visual arrays represented as separate images or as a combined image in visual short-term memory (VSTM)? Proponents of the integration account suggest that an image of the first array is gradually formed and integrated with an image of the second to produce a combined representation. This view is evidenced by successful performance in an empty-cell detection task. In this task, on a 4 x 4 square matrix, 7 locations are occupied on a first array, followed by a variable interval, and then by 8 other occupied locations on a second array. Subjects' success in identifying the remaining empty cell has been taken as evidence for integration. In this study, we show that success in this task can be better accounted for by a convert-and-compare process than by an integration process. We conclude that VSTM only supports limited integration across sequential arrays.     

Effects of perceptual quality and visual field of probe stimulus presentation on memory search for letters

Observers indicated whether a single probe letter presented to the left visual field/right hemisphere (LVF-RH) or to the right visual field/left hemisphere (RVF-LH) was contained in a memory set of 2, 3, 4, or 5 letters. For positive trials, the increase in reaction time caused by perceptually degrading the probe letter became progressively larger as memory set size became larger when the probe was presented to the LVF-RH but not when the probe was presented to the RVF-LH. These results were obtained regardless of whether the case of the probe letter varied randomly (Experiment 1) or only capital letters were used (Experiment 2). The results on LVF-RH trials suggest a relatively visuospatial memory comparison process, whereas the results on RVF-LH trials suggest a more abstract memory comparison process. In addition to these effects, the intercept of the memory set size function was lower on LVF-RH trials than on RVF-LH trials when the probe letter was perceptually degraded, consistent with the hypothesis that the right hemisphere is more efficient than the left at early visuospatial processes. Perhaps it is this efficiency at early visuospatial processes that produces the bias toward visuospatial memory comparison on LVF-RH trials.     

Effects of task-irrelevant grouping on visual selection in partial report

Perceptual grouping modulates performance in attention tasks such as partial report and change detection. Specifically, grouping of search items according to a task-relevant feature improves the efficiency of visual selection. However, the role of task-irrelevant feature grouping is not clearly understood. In the present study, we investigated whether grouping of targets by a task-irrelevant feature influences performance in a partial-report task. In this task, participants must report as many target letters as possible from a briefly presented circular display. The crucial manipulation concerned the color of the elements in these trials. In the sorted-color condition, the color of the display elements was arranged according to the selection criterion, and in the unsorted-color condition, colors were randomly assigned. The distractor cost was inferred by subtracting performance in partial-report trials from performance in a control condition that had no distractors in the display. Across five experiments, we manipulated trial order, selection criterion, and exposure duration, and found that attentional selectivity was improved in sorted-color trials when the exposure duration was 200 ms and the selection criterion was luminance. This effect was accompanied by impaired selectivity in unsorted-color trials. Overall, the results suggest that the benefit of task-irrelevant color grouping of targets is contingent on the processing locus of the selection criterion.     

Improving visual short-term memory by sequencing the stimulus array

When multiple objects are presented briefly and simultaneously in a visual array, visual short-term memory (VSTM) can maintain only a limited number of these items. The present research report reveals that splitting the to-be-remembered items into two sequential arrays significantly increases VSTM performance relative to the simultaneous presentation of the same items. A memory benefit also emerges when the full object array is flashed twice (repeated) rather than being presented continuously for the same duration. Moreover, the sequential and repetition benefits are specifically pronounced for individuals with low performance for simultaneously presented items. Our results suggest that the conventional, simultaneous presentation mode may underestimate VSTM performance due to attentional limitations and/or competition between stimulus representations. In contrast, temporal segregation of the stimulus input may help participants maximize their performance and utilize their full VSTM capacity.     

Comparisons of memory for nonverbal auditory and visual sequential stimuli

Properties of auditory and visual sensory memory were compared by examining subjects' recognition performance of randomly generated binary auditory sequential frequency patterns and binary visual sequential color patterns within a forced-choice paradigm. Experiment 1 demonstrated serial-position effects in auditory and visual modalities consisting of both primacy and recency effects. Experiment 2 found that retention of auditory and visual information was remarkably similar when assessed across a 10 s interval. Experiments 3 and 4, taken together, showed that the recency effect in sensory memory is affected more by the type of response required (recognition vs. reproduction) than by the sensory modality employed. These studies suggest that auditory and visual sensory memory stores for nonverbal stimuli share similar properties with respect to serial-position effects and persistence over time.     

Perceptual grouping boosts visual working memory capacity and reduces effort during retention

Consistent, robust boosts to visual working memory capacity are observed when colour–location arrays contain duplicate colours. The prevailing explanation suggests that duplicated colours are encoded as one perceptual group. If so, then we should observe not only higher working memory capacity overall for displays containing duplicates, but specifically an improved ability to remember unique colours from displays including duplicates compared with displays comprising all uniquely coloured items. Furthermore, less effort should be required to retain displays as colour redundancy increases. I recorded gaze position and pupil sizes during a visual change detection task including displays of 4–6 items with either all unique colours, two items with a common colour, or three items with a common colour in samples of young and healthy elderly adults. Increased redundancy was indeed associated with higher estimated working memory capacity, both for tests of duplicates and uniquely coloured items. Redundancy was also associated with decreased pupil size during retention, especially in young adults. While elderly adults also benefited from colour redundancy, spillover to unique items was less obvious with low redundancy than in young adults. This experiment confirms previous findings and presents complementary novel evidence linking perceptual grouping via colour redundancy with decreased mental effort.     

Testing visual short-term memory: Simultaneous versus sequential presentations

Two experiments testing immediate ordered recall are presented; in these experiments, subjects engaged in repetitive speech (“articulatory suppression”) during a visual presentation in order to prevent auditory recoding of the stimuli. In both experiments, a simultaneous presentation produced results that suggested the use of visual short-term memory, whereas a sequential presentation did not. In Experiment 1, visual confusion errors occurred more often than would be expected by chance for a simultaneous presentation but not for a sequential presentation. In Experiment 2, recall from visual short-term memory was expected to suffer more when subjects wrote a prefix than when they spoke a prefix; this effect occurred for a simultaneous presentation but not for a sequential presentation. These results suggest that existence of a visual short term store that retains a simultaneous presentation but not a sequential presentation.     

Effects of grouping on the pupillary response in a short-term memory task

Subjects heard strings of nine digits for immediate recall, either at a monotone 1/sec. rate or in groups of three digits separated by pauses. Concurrent measurements of pupil size show a steady dilation in the monotone condition, and brief dilation-constriction waves during the pauses of grouped presentation. The results are consistent with hypotheses concerning rehearsal in the two modes of presentation. Pupillary dilations apparently accompany episodes of covert rehearsal.     

Effects of memory load on visual search

It remains unclear how memory load affects attentional processes in visual search (VS). No effects, as well as beneficial and detrimental effects of memory load, have been found in this type of task. The main goal of the present research was to explore whether memory load has a modulating effect on VS by means of a different attentional set induced by the order of trials (mixed vs. blocked) and by the time presentation of visual display (long vs. short). In Experiment 1, we randomized the order of type of trial (5, 10 and 15 items presented in the display) while it remained constant (10 items) in Experiments 2A and 2B. In the later experiments, we also changed time presentation of visual display (3000 vs. 1300 ms, respectively). Results showed no differential effects of memory load in Experiments 1 and 2A, but they showed up in Experiment 2B: RTs were longer in the attentional task for trials under high memory load conditions. Although our hypothesis of the attentional set is supported by the results, other theoretical implications are also worth discussing in order to better understand how memory load may modulate attentional processes in VS.     

Effects of stimulus duration and choice delay on visual categorization in pigeons

We [Lazareva, O. F., Freiburger, K. L., & Wasserman, E. A. (2004). Pigeons concurrently categorize photographs at both basic and superordinate levels. Psychonomic Bulletin and Review, 11, 1111-1117] previously trained four pigeons to classify color photographs into their basic-level categories (cars, chairs, flowers, or people) or into their superordinate-level categories (natural or artificial). Here, we found that brief stimulus durations had the most detrimental effect on the basic-level discrimination of natural stimuli by the same pigeons. Increasing the delay between stimulus presentation and choice responding had greater detrimental effect on the basic-level discrimination than the superordinate-level discrimination. These results suggest that basic-level discriminations required longer stimulus durations and were more subject to forgetting than were superordinate-level discriminations. Additionally, categorization of natural stimuli required longer stimulus durations than categorization of artificial stimuli, but only at the basic level. Together, these findings suggest that basic-level categorization may not always be superior to superordinate-level categorization and provide additional evidence of a dissociation between natural and artificial stimuli in pigeons’ categorization.     

Unifying sequential effects in perceptual grouping

Temporally-extended perception involves a delicate balance of constancy and change. 'This can be seen, for instance, when viewing bistable figures such as the Necker cube. A recent study by Gepshtein and Kubovy of sequential effects in multistable dot lattices demonstrates constancy and change within the same set of data. They propose that these opposing trends might be explained by the same single factor: a persistent random orientation bias that is intrinsic to brain activity. This proposal could form the basis for a new account of multistability.     

Some further studies on the effect of grouping elements of a visual stimulus on the cortical evoked potential

Grouping elements of a visual stimulus is shown to reduce the amplitude of the bipolar occipital evoked potential in three experiments. The first shows similar effects of grouping elements on the horizontal and vertical dimensions, combining in a nearly additive manner. The second shows a less stable grouping effect using irregularly spaced lines as stimuli. In the third experiment, small deviations from uniformity are seen to produce a reliable attenuation of the cortical evoked potential.     

The effect of change in sequential visual stimuli on GSR adaptation: II,the novel stimulus as a disinhibiting stimulus

GSR records were obtained for 20 Ss presented with a series of 80 stimuli (four lights alternating in apparent random sequence). Records were obtained, also, for 20 Ss in each of two groups, using the same procedure: in Group 1, a tone was substituted for one of the lights, early in the sequence, and in Group 2, it was substituted later in the sequence. The tone, the novel stimulus, produced significant changes in the GSR adaptation patterns of the two groups.     

Effects of variations in force and stimulus uncertainty on fractionated reaction time.

Previous research has shown that reaction time (RT) and premotor time varied as a function of force even in simple-RT paradigm. The present purpose was to examine whether stimulus uncertainty induced by catch trials would cause programming delay until after the signal to respond. Subjects were required to react and produce a designated peak force as soon as possible after a visual stimulus, with and without catch trials. Five different levels of force were 10, 30, 50, 70, and 90% of the maximum grip strength of subjects. Analysis showed that simple RT and premotor time changed as a function of force, regardless of whether catch trials were removed. These findings suggest that stimulus uncertainty is not a necessary condition for programming delay.     

Effects of stimulus variability on perception and representation of spoken words in memory

A series of experiments was conducted to investigate the effects of stimulus variability on the memory representations for spoken words. A serial recall task was used to study the effects of changes in speaking rate, talker variability, and overall amplitude on the initial encoding, rehearsal, and recall of lists of spoken words. Interstimulus interval (ISI) was manipulated to determine the time course and nature of processing. The results indicated that at short ISIs, variations in both talker and speaking rate imposed a processing cost that was reflected in poorer serial recall for the primacy portion of word lists. At longer ISIs, however, variation in talker characteristics resulted in improved recall in initial list positions, whereas variation in speaking rate had no effect on recall performance. Amplitude variability had no effect on serial recall across all ISIs. Taken together, these results suggest that encoding of stimulus dimensions such as talker characteristics, speaking rate, and overall amplitude may be the result of distinct perceptual operations. The effects of these sources of stimulus variability in speech are discussed with regard to perceptual saliency, processing demands, and memory representation for spoken words.