Interaction between perceived and imagined rotation

In Experiment 1, subjects performed a mental-rotation task in which they were timed as they decided whether rotated letters were normal or backwards. Between presentations of the letters, they watched a rotating textured disk that induced an aftereffect of rotary movement on the letters. The function relating reaction times to orientation was influenced asymmetrically by the aftereffect, suggesting that perceived movement interacts with imagined movement. Experiment 2 showed that the aftereffect produced a negligible influence on perceived orientation, suggesting that the influence of the aftereffect on mental rotation was not caused by changes in the perceived orientations of the letters. Detailed analysis of the mental-rotation functions suggested that the aftereffect may sometimes have induced subjects to rotate letters through the larger rather than the smaller angle back to the upright where the aftereffect was in the appropriate direction.     

Reaction time to a word in different orientations with letters rotated separately in different orientations

Six men and six women were timed as they made judgments about a word whose line of letters and individual letters were separately turned in different angular orientations. The subjects were asked to indicate by manual key-pressing responses whether the letters in the word were normal letters or reflected, mirror-image letters. Analysis showed that (1) reaction time (RT) was slower for reflected letters than for normal letters, and for subjects using the left (nondominant) hand rather than the right (dominant) hand for responding to normal letters. (2) RT generally increased in relation to the deviation of the individual letters from normal upright orientation but increased more reliably for normal than for reflected letters. (3) Although there were exceptions, RT for words composed of normal letters generally increased in relation to the deviation of the individual letters from normal upright, regardless of the orientation of the line of letters.     

Developmental differences in mental rotation.

A reaction time paradigm was used to investigate developmental differences in ability to rotate and compare imaginal representations. Third grade, fifth grade, and college students (ages 9, 11, and 20 years, respectively) were required to determine whether a letter of the alphabet was presented in its backward or normal position. Letters were presented at 0, 60, 120, 180, 240, or 300° orientations from upright. Subjects were given no advance information about a test letter, or they were given identity and orientation information. In the no information condition, reaction time increased for all age groups as a function of the departure in orientation of the test letter from an upright position. In the advance information condition, reaction time remained uniform across orientation for only the college subjects. The developmental implications of these findings are discussed.     

The effect of familiarity on the processing of fragmented figures

The processing of fragmented figures was investigated in a same-different reaction time task with pairs of intact and pairs of fragmented alphabet letters. The effect of fragmentation was significantly larger for pairs of letters rotated into an unfamiliar orientation than for pairs of normally oriented letters. Since this significant interaction was obtained for subjects emphasizing a structural mode of processing (Hock, 1973), it was concluded that familiarity had a direct effect on the structural/ organizational processing of the fragmented figures.     

Winding one's ps and qs: mental rotation and mirror-image discrimination

Subjects were timed as they made judgments about ps and qs (also interpretable as ds and bs) in different angular orientations. Whether these judgments were left-right mirror-image discriminations (b vs. d or p vs. q) or up-down mirror-image discriminations (b vs. p or d vs. q), the subjects' reaction times increased sharply with the angular departure of each letter from its designated normal upright orientation, a fact implying mental rotation. This was so whether the subjects responded with the letter labels themselves (e.g., b vs. d) or with the labels left versus right or top versus bottom. It was again the case when the letters were replaced by nonletter forms, in which event there was also a left visual-field advantage in reaction time. This study is therefore the first to demonstrate a mental-rotation strategy when the canonical forms to be discriminated are up-down mirror images as well as when they are left-right mirror images. In both cases, however, the task requires the ability to tell left from right, and we suggest that this is the critical ingredient that induces mental rotation.     

Orientation congruency effects in visual search.

Subjects searched for the letter E in a background of Ls and Fs in displays that had 1, 2, 4, 8, or 12 letters. The letters could be shown at one of six orientations (upright or rotated clockwise in 60 degrees increments). The displays were either congruent for orientation (all letters had the same orientation) or incongruent (letters in haphazard orientations except for the target on E-present trials). Search time increased linearly with the number of letters in the display, and more so for E-absent trials than for E-present trials. Letter orientation, in general, increased search time and produced an M-shaped function. Furthermore, orientation effects were attenuated in congruent displays relative to those produced by incongruent displays. The results demonstrated systematic orientation effects on the time to search for a simple pattern embedded in simple backgrounds, and provided converging evidence for the orientation-congruency effect found by Jolicoeur (1990b, Journal of Experimental Psychology: Human Perception and Performance, 16, 351-364).     

Orientation congruency effects on the identification of disoriented shapes

Effects of orientation on identification can be attenuated when other patterns at the same (or a similar) orientation are identified in close temporal contiguity. In Experiments 1 and 2, letters were presented simultaneously in brief masked displays. Identification accuracy was much higher when the letters had consistent orientations than when the letters had different orientations within a display. In Experiment 3, two letters were presented sequentially. Identification accuracy was higher with congruent than with incongruent orientations. The results are unexpected if one assumes that the patterns themselves are rotated until upright prior to their identification, unless pattern rotation processes can be primed, and that priming requires orientation congruence between the priming and primed stimulus. The results are expected if the orientation of a frame of reference can be adjusted to the orientation of the patterns during the identification process.     

Controlled and automatic processing during mental rotation

In two experiments, 9- and 10-year-olds and adults were tested on a mental rotation task in which they judged whether stimuli presented in different orientations were letters or mirror-images of letters. The mental rotation task was performed alone on 48 trials and concurrently with a memory task on 48 additional trials. The concurrent memory task in Experiment 1 was recalling digits; in Experiment 2, recalling positions in a matrix. The key result was that the slope of the function relating response time to stimulus orientation was the same when the mental rotation task was performed alone and when performed concurrently with the memory task. This result is interpreted as showing that mental rotation is an automatic process for both children and adults.     

Imagining and naming rotated natural objects

The present experiment examined whether subjects can form and store imagined objects in various orientations. Subjects in a training phase named line drawings of natural objects shown at six orientations, named objects shown upright, or imagined upright objects at six orientations. Time to imagine an upright object at another orientation increased the farther the designated orientation was from the upright, with faster image formation times at 180° than at 120°. Similar systematic patterns of effects of orientation on identification time were found for rotated objects. During the test phase, all subjects named the previously experienced objects as well as new objects, at six orientations. The orientation effect for old objects seen previously in a variety of orientations was much reduced relative to the orientation effect for new objects. In contrast, substantial effects of orientation on naming time were observed for old objects for subjects who had previously seen the objects upright only or upright but imagined at different orientations. The results suggest that the attenuation of initially large effects of orientation with practice cannot be due to imagining and forming representations of objects at a number of orientations.     

Flexible mental processes in numerical size judgments: The case of hebrew letters that are used to convey numbers

In addition to its primary linguistic function, the Hebrew alphabet is sometimes used as a means of number notation (i.e., the system of gematria). Hebrew letters, Arabic numerals, Hebrew number names, and Hebrew letter names were used in a numerical size comparison task, in which two visually presented symbols were compared for numerical value while irrelevant variations in their physical size had to be ignored. A size congruity effect, indicated by faster responses when differences in physical and numerical size were consistent, was larger for Arabic numerals than for number names. The effect for Hebrew letters was similar to that for Arabic numerals and was stronger than that observed for letter names. These results suggest flexible processing of Hebrew letters, so that they function as ideographic symbols in an arithmetic context. A distance effect, indicated by an inverse relationship between reaction time and numerical distance, was found for all notations but was particularly strong for Hebrew letters.     

Mental rotation in perspective problems

The present paper demonstrates that mental rotation as used in the processing of disoriented objects (Cooper and Shepard 1973) can also be used as an explanatory concept for the processing of perspective problems in which the task is to imagine how an environment will appear from another vantage point. In a cognitive map, subjects imagined an initial line of vision and subsequently processed a reorientation stimulus, requesting them to imagine a turn over 0, 45, 90, 135, or 180 degrees. Time for a reorientation increased linearly with the size of the imaginary turn up to 135 degrees and decreased for turns of 180 degrees; apparently, about-faces were relatively easy to imagine. The increment of reorientation time between 0 and 135 degrees was larger for maps presented in unfamiliar orientations such as South-West up. Both the increment and the interaction with familiarity are consistent with an explanation in terms of mental rotation.     

Reference frames in mental rotation

Four experiments are reported that investigate whether images or reference frames are transformed during a mental rotation task. In all experiments a display of four identical letters (P1) was presented at either +90 degrees or -90 degrees from upright, and subjects had to decide whether the letters were normal or mirror-image reflections. A single letter (P2) was then presented 100 ms later in a variable orientation with the same task instructions. Reaction times to P2 were assessed to determine whether an image of P2 was rotated to upright or whether an internal reference frame was rotated into congruence with P2 from the orientation of P1. The results as a whole suggest that transformations of P2 can be initiated either relative to upright or relative to the orientation of P1. They further indicate that the probability of using each reference orientation can be changed by procedural variations. The findings are most parsimoniously interpreted as suggesting that mental rotation involves the transformation of reference frames rather than the transformation of template-like representations.     

Identification of disoriented objects: effects of context of prior presentation

Half of the subjects in the training phase of Experiment 1 named objects shown in a number of orientations, whereas the other half named objects shown upright only. All subjects named objects seen in a number of different orientations in the transfer phase. Half of the objects in the transfer phase were the ones they had seen in the training phase (old objects), whereas the other half were objects they had not seen before (new objects). Mean naming time in the transfer phase increased more as the objects were rotated further from the upright for new objects than for old objects when the old objects had been seen in a variety of orientations. In contrast, a substantial and equivalent orientation effect on identification time was obtained for old and new objects when the old objects had been seen upright only. These results suggest that the extraction and use of orientation-invariant attributes to identify objects is not a "default" identification strategy employed by the human visual system. In Experiment 2, half of the objects named in the training phase were shown upright only, whereas the other half were shown in a number of orientations. Both types of objects (upright vs. rotated) were presented in a mixed fashion from trial to trial. The results revealed that prior naming of the objects in this context resulted in equivalent reductions in the magnitude of the orientation effect on identification time for both sets of objects (upright and rotated). Together, the results of these two experiments suggest that markedly different representations of objects are encoded, depending on the context in which objects are seen. Implications for models of pattern recognition are discussed.     

Orientation specificity in biological motion perception

We addressed the issue of how display orientation affects the perception of biological motion. In Experiment 1, spontaneous recognition of a point-light walker improved abruptly with image-plane display rotation from inverted to upright orientation. Within a range of orientations from 180 degrees to 90 degrees, it was dramatically impeded. Using ROC analysis, we showed (Experiments 2 and 3) that despite prior familiarization with a point-light figure at all orientations, its detectability within a mask decreased with a change in orientation from upright to a range of 90 degrees-180 degrees. In Experiment 4, a priming effect in biological motion was observed only if a prime corresponded to a range of deviations from upright orientation within which the display was spontaneously recognizable. The findings indicate that display orientation nonmonotonically affects the perception of biological motion. Moreover, top-down influence on the perception of biological motion is limited by display orientation.     

Orientation unbound: Dissociation of identity and orientation under rapid serial visual presentation

Participants were shown rapid sequences of three letters, flanked by digits, each rotated 0 degree, 90 degrees, 180 degrees, or 270 degrees clockwise from upright. In Experiment 1, the participants tried to report the letter that matched the orientation of an arrow, presented either before (before task) or after (after task) the sequence. A third task (total task) required them to report all of the letters. Accuracy for individual letters was significantly better in the total task than in the before task, and better in the before task than in the after task, suggesting particular difficulty in binding orientation to identity. In Experiment 2, the participants were given letter probes and were asked to indicate the orientation of the probed letter. Although report was above chance, there were frequent illusory conjunctions. Since perception of orientation must depend on prior establishment of identity, our results suggest that orientation and identity may become unbound during processing and are held in parallel storage systems.     

On how adults identify the orientation of a shape

It is generally assumed that the orientation of a shape is judged only by identifying the location of a particular feature. In contrast, it is argued here that the basis of orientation judgments depends on the task; this proposal is examined for judgments of upside down and sideways. Pictures of mono-oriented objects were presentedone at a time, and adults identified the orientations of each in a RT paradigm. One condition presented successively upright and upside-down pictures or upright and sideways pictures. Another condition presented successively upside-down and sideways pictures. As predicted, the time to identify orientation was longer for the condition presenting two nonuprights, because specific identifications of upside down and sideways were required, whereas the other condition required only that uprightness be distinguished from nonuprightness. The notion that the nature of a judgment of shape orientation depends on the contrasts provided by the task has implications for theory and experimental design that are discussed for both realistic and geometric shapes.     

Limited transfer of subliminal response priming to novel stimulus orientations and identities

Recently, priming effects of unconscious stimuli that were never presented as targets have been taken as evidence for the processing of the stimuli's semantic categories. The present study explored the necessary conditions for a transfer of priming to novel primes. Stimuli were digits and letters which were presented in various viewer-related orientations (upright, horizontal, inverted). The transfer of priming to novel stimulus orientations and identities was remarkably limited: in Experiment 1, in which all conscious targets stood upright, no transfer to unconscious primes in a non-target orientation was found. Experiment 2, in which primes were presented without masks, ruled out the possibility that primes were presented too short to allow congruency effects. In Experiments 3 and 4, in which all targets were presented upside down, priming transferred to upright stimuli with target identities but neither to horizontal stimuli nor to stimuli with novel identities. We suggest that whether a transfer of priming to unpracticed stimuli occurs or not depends on observers' expectations of specific stimulus exemplars.     

Mental rotation: effects of dimensionality of objects and type of task

The original studies of mental rotation estimated rates of imagining rotations that were much slower when two simultaneously portrayed three-dimensional shapes were to be compared (R. Shepard & J. Metzler) than when one two-dimensional shape was to be compared with a previously learned two-dimensional shape (Cooper and her associates). In a 2 X 2 design, we orthogonally varied dimensionality of objects and type of task. Both factors affected reaction times. Type of task was the primary determiner of estimated rate of mental rotation, which was about three times higher for the single-stimulus task. Dimensionality primarily affected an additive component of all reaction times, suggesting that more initial encoding is required for three-dimensional shapes. In the absence of a satisfactory way of controlling stimulus complexity, the results are at least consistent with the proposal that once three-dimensional objects have been encoded, their rotation can be imagined as rapidly as the rotation of two-dimensional shapes.     

Global-local orientation congruency effects in visual search

In a visual search task, subjects had to decide which of 2 possible target letters was presented among 12 distractor letters. The 13 characters were arranged to form a global Navon-type letter. The global letter and the local letters (target and distractors) were independently presented in four different viewer-related orientations. When the global letter and the target were frequently congruently oriented, the response times increased with growing orientation disparity between them. This global-target congruency effect was independent from target identity (Experiment 1), and it diminished when global and target orientations were not correlated (Experiment 2). The results indicate that the orientation of the global letter can be deliberately used in order to facilitate the processing of congruently oriented local targets. The alignment of a spatial frame of reference is discussed as the most probable process underlying this facilitation.     

Mental rotation of mirrored letters: evidence from event-related brain potentials

Event-related brain potentials (ERPs) were recorded while participants (n=13) were presented with mirrored and normal letters at different orientations and were asked to make mirror-normal letter discriminations. As it has been suggested that a mental rotation out of the plane might be necessary to decide on mirrored letters, we wanted to determine whether this rotation occurs after the plane rotation in mirror rotated letters. The results showed that mirrored letters in the upright position elicited a negative-going waveform over the right hemisphere in the 400-500 ms window. A similar negativity was also present in mirrored letters at 30 degrees, 60 degrees, and 90 degrees, but in these cases it was delayed. Moreover, the well-known orientation effect on the amplitude of the rotation-related negativity was also found, although it was more evident for normal than for mirrored letters. These results indicate that the processing of mirrored letters differs from that of normal letters, and suggest that a rotation out of the plane after the plane rotation may be involved in the processing of mirror rotated letters.