The effects of stimulus set size and word frequency on verbal serial recall

Two experiments are reported which examine immediate serial recall for high-and low-frequency words. The words in each list were either repeatedly drawn from the same small pool of candidates (in the closed set conditions) or each word only ever occurred once during the experiment (in the open set conditions). The results consistently show an effect of word frequency but the effect of set size was only apparent for low-frequency words. It is argued that both frequency and set size effects reflect processes concerning the “clean-up” of degraded short-term memory traces.     

The effects of stimulus set size and word frequency on verbal serial recall

Two experiments are reported which examine immediate serial recall for high- and low-frequency words. The words in each list were either repeatedly drawn from the same small pool of candidates (in the closed set conditions) or each word only ever occurred once during the experiment (in the open set conditions). The results consistently show an effect of word frequency but the effect of set size was only apparent for low-frequency words. It is argued that both frequency and set size effects reflect processes concerning the "clean-up" of degraded short-term memory traces.     

The effects of memory set size and information structure on learning and retention

Two experiments examined the effects of memory set size and information structure on learning and retention. Participants learned 48 (small set) or 144 (large set) facts about individuals, and were tested over 48 facts. The test facts included either 4 facts about 12 individuals (12-person condition) or 12 facts about 4 individuals (4-person condition). During learning, there was an advantage for the small-set group in the 4-person condition, but a disadvantage in the 12-person condition. During testing, there was an advantage for the 4-person condition relative to the 12-person condition for the small-set group, even when the conditions were equated in terms of name exposure. The results support a mental model account of memory representation and retrieval.     

The effect of visual frame of reference on a judgement of plane stimulus orientation by children

Three studies are reported with children aged 4 1/2 to 9 1/2 years and also with educationally subnormal children, in which it was found that up to about 7 years children's selection of one of a pair of line stimuli as 'falling over' is affected by the nature of the visual surround contours provided. Both the form of the stimulus surround and the presence or absence of a baseline tilted 45 degrees relative to the horizontal were found to affect the children's judgements. The plane (horizontal or vertical) in which the stimuli were presented had no effect on the results. It is argued that while the results show the influence of the visual surround on children's comprehension of 'falling over', this may not be wholly explicable in terms of surround contour matching, as conventionally correct judgements were obtained in the absence of all straight line contours in the immediate surround.     

Brain activity during the encoding, retention, and retrieval of stimulus representations

Studies of delayed nonmatching-to-sample (DNMS) performance following lesions of the monkey cortex have revealed a critical circuit of brain regions involved in forming memories and retaining and retrieving stimulus representations. Using event-related functional magnetic resonance imaging (fMRI), we measured brain activity in 10 healthy human participants during performance of a trial-unique visual DNMS task using novel barcode stimuli. The event-related design enabled the identification of activity during the different phases of the task (encoding, retention, and retrieval). Several brain regions identified by monkey studies as being important for successful DNMS performance showed selective activity during the different phases, including the mediodorsal thalamic nucleus (encoding), ventrolateral prefrontal cortex (retention), and perirhinal cortex (retrieval). Regions showing sustained activity within trials included the ventromedial and dorsal prefrontal cortices and occipital cortex. The present study shows the utility of investigating performance on tasks derived from animal models to assist in the identification of brain regions involved in human recognition memory.     

A comparison of stimulus set size on tact training for children with autism spectrum disorder

Previous studies on skill acquisition have taught targets in stimulus sets composed of different numbers of stimuli. Although the rationale for selection of a stimulus set size is not clear, the number of target stimuli trained within a set is a treatment decision for which there is limited empirical support. The current investigation compared the efficiency of tact training in 4 stimulus set sizes, each of which included 12 stimuli grouped into (a) 4 sets of 3 stimuli, (b) 3 sets of 4 stimuli, (c) 2 sets of 6 stimuli, and (d) 1 set of 12 stimuli. Results of all 4 participants with autism spectrum disorder show tact training with larger (i.e., 6 and 12) stimulus set sizes was more efficient than training with smaller (i.e., 3 and 4) stimulus set sizes.     

Perception of biological motion: A stimulus set of human point-light actions

We present a set of stimuli representing human actions under point-light conditions, as seen from different viewpoints. The set contains 22 fairly short, well-delineated, and visually “loopable” actions. For each action, we provide movie files from five different viewpoints as well as a text file with the three spatial coordinates of the point lights, allowing researchers to construct customized versions. The full set of stimuli may be downloaded fromwww.psychonomic.org/archive/.     

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.     

Reversed better-than-average effect in direct comparisons of nonsocial stimuli depends on the set size

Studies on direct comparative judgments typically show that, for items that are positively evaluated, a single item randomly drawn from a larger set of similar items tends to be judged as better than average (the BTA effect). However, Windschitl, Conybeare, and Krizan (2008) demonstrated that, under timing conditions that do not favor focusing attention on the single item, the reversal of the BTA effect occurs. We report two experiments showing that the magnitude of the reversed BTA effect increases as a function of the size of a multiitem referent with which a single item target is compared. Specifically, in direct comparative judgments of the attractiveness of positively evaluated objects (nice-looking cloth buttons, attractive buildings, or cupcakes), underestimation of the attractiveness of singletons, as compared with a multiitem set (reversed BTA effect), increased with the increased set size. Analysis of absolute judgments obtained for singletons and for small and large multiitem sets suggests that, for attractive stimuli, both the reversed BTA effect in comparative judgments and its sensitivity to set size occur as a result of a positive relationship between set size and perceived attractiveness in absolute judgments.     

Perception of biological motion: a stimulus set of human point-light actions.

We present a set of stimuli representing human actions under point-light conditions, as seen from different viewpoints. The set contains 22 fairly short, well-delineated, and visually "loopable" actions. For each action, we provide movie files from five different viewpoints as well as a text file with the three spatial coordinates of the point lights, allowing researchers to construct customized versions. The full set of stimuli may be downloaded from www.psychonomic.org/archive/.     

Inferring intentions from biological motion: A stimulus set of point-light communicative interactions

We present the first database of communicative interactions reproduced through point-light displays (Communicative Interaction Database). The database contains 20 communicative interactions performed by male and by female couples. For each action, we provide movie files from four different viewpoints, as well as text files with the 3-D spatial coordinates of the point lights, allowing researchers to construct customized versions. By including various types of actions performed with different social motives, the database contains a diverse sample of nonconventional communicative gestures. Normative data collected to assess the recognizability of the stimuli suggest that, for most action stimuli, information in point-light displays is sufficient for clear recognition of the action as communicative, as well as for identification of the specific communicative gesture performed by the actor. The full set of stimuli may be downloaded from http://brm.psychonomic-journals.org/ content/supplemental and from http://ppw.kuleuven.be/labexppsy/lepSite/resources/CID.rar.     

Change of a frame of reference with velocity in visual motion perception

The present study examined how a frame of reference was affected by velocity. This question was examined with respect to a system consisting of two points: one moved rectilinearly with constant velocity, and the other moved on a track in the shape of a cycloid (defined as the movement of two points—one on the hub and the other on the rim of a rolling wheel). The results indicated that (1) a frame of reference in which the centroid of the total picture was stationary was chosen mainly in a low-velocity range (0.1–0.7 deg/sec), (2) a frame of reference in which a picture point moved rectilinearly was chosen mainly in a medium-velocity range (0.8–40.0 deg/sec), and (3) an absolute coordinate system was chosen mainly in a high-velocity range (>40.0 deg/sec). The current evidence and other findings seem to be consistent with the idea that groups of neurons related to the three frames of reference are independent of one another, that the velocity ranges of the groups of neurons roughly overlapped each other, and that the most salient frame of reference is chosen (i.e., exclusion principle in choice of a frame of reference).     

The reference frame of figure-ground assignment

Figure-ground assignment involves determining which visual regions are foreground figures and which are backgrounds. Although figure-ground processes provide important inputs to high-level vision, little is known about the reference frame in which the figure's features and parts are defined. Computational approaches have suggested a retinally based, viewer-centered reference frame for figure-ground assignment, but figural assignment could also be computed on the basis of environmental regularities in an environmental reference frame. The present research used a newly discovered cue, lower region, to examine the reference frame of figure-ground assignment. Possible reference frames were misaligned by changing the orientation of viewers by having them tilt their heads (Experiments 1 and 2) or turn them upside down (Experiment 3). The results of these experiments indicated that figure-ground perception followed the orientation of the viewer, suggesting a viewer-centered reference frame for figure-ground assignment.     

The development of visual encoding and retention skills

The development of the ability to visually encode and maintain a visual stimulus was examined in a paradigm in which verbal encoding of the stimulus was prevented. The 8-, 12-, and 21-year-old subjects participated in a shadowing task during which they viewed a letter which was visually presented for 200 msec, 5 sec after the shadowing list began. On each trial subjects either reported the letter immediately after presentation or continued shadowing for 4 or 10 sec. Although results replicated those found in previous research using the paradigm, no age differences were found in recall accuracy, types of errors, or introspective reports describing perceived recall strategy. These findings suggest that even 8 year olds were able to employ a visual code and retain it for several seconds in a situation in which incentive to do so was provided.     

The time-based word length effect and stimulus set specificity

The word length effect is the finding that short items are remembered better than long items on immediate serial recall tests. The time-based word length effect refers to this finding when the lists comprise items that vary only in pronunciation time. Three experiments compared recall of three different sets of disyllabic words that differed systematically only in spoken duration. One set showed a word length effect, one set showed no effect of word length, and the third showed a reverse word length effect, with long words recalled better than short. A new fourth set of words was created, and it also failed to yield a time-based word length effect. Because all four experiments used the same methodology and varied only the stimulus sets, it is argued that the time-based word length effect is not robust and as such poses problems for models based on the phonological loop.     

The effects of endogenous attention and stimulus onsets on encoding target location

The effects of endogenously attended and non-attended stimulus onsets on spatial stimulus encoding of a target were explored in a Simon task. In each experiment participants made speeded left or right key-press responses to the colour of a target that followed a cueing display consisting of several shapes. The target appeared within some shapes and not others. The target's spatial code as measured by a Simon task was its location relative to possible target positions and relative to the centre of the display. Target location was not coded relative to the positions of onset shapes that could not contain a target. These spatial coding effects were found at cue-target intervals of 50, 300, and 1000 ms. The data indicate that target location is defined relative to the distribution of endogenous attention and reference frames aligned with the centre of the display and that the spatial code assigned to a target is not affected when attention is shifted in the target's direction.