Memory psychophysics

Summary The relationship between perceptual and cognitive processes has been a topic of increasing interest. This review focuses on the use of techniques and theory drawn from classical psychophysics and applied to the study of mental representation. Several issues including examination of the functions that relate remembered and perceived magnitude to physical intensity, the relationship of memorial to perceptual functions, the effect of time on the memorial function, considerations in the methodology of memory psychophysics experiments, the level of functional equivalence between memorial and perceptual representation, and the use of psychophysical techniques and theory in the study of visual imagery are addressed. While the data suggest that the relationship between remembered magnitude and physical intensity and between perceived magnitude and physical intensity can be described by power functions, a model capable of accounting for the behavior of the memory magnitude for all stimulus dimensions and at all time intervals has not yet been found. Several unresolved issues and typical difficulties with research in memory psychophysics are also discussed.     

Memorial psychophysics for visual area: The effect of retention interval

Previous studies (e.g., Kerst & Howard, 1978) have shown that remembered visual areas are related to actual areas by a more compressive power function than are perceived visual areas. Experiment 1 useda between-groups design to replicate this effect for a map of Europe and showed that compression increased as the retention interval, the time between map inspection and area estimation, increased from 2 min to 1 week. Experiment 2 obtained similar results with a similar design, except that a simple two-region map was used to reduce uncertainty. Overall, the results suggest that two processes may be operating: uncertainty and gradual transformation of the representation of the map in memory.     

Calibration of a color monitor for visual psychophysics

It has become common for stimuli used in visual psychophysical experiments to be presented on high-resolution color cathode-ray tubes (CRTs) such as the Barco CDCT 6551. These enable a flexibility of color, spatial-frequency content, temporal-frequency content, duration, size, and position that is not provided by most other media. CRTs are, however, not perfect; they suffer from the effects of temporal instability, spatial variability, lack of phosphor constancy, gun interdependence, and gun nonlinearity. This paper describes methods of assessing these aspects of monitor performance with respect to how significant each may be in psychometric terms. Although every application of CRT use in visual psychophysics is different, some general rules can be formulated to help ensure that unwanted effects are kept to a minimum. For the CRT used in this study (Barco CDCT 6551), a warm-up time of 30-45 min is necessary before chromatic and luminous stability ensues. Restriction of individual gun outputs to within 10%-90% of the possible range ensures that the effects of gun interdependence and lack of phosphor constancy are negligible. Calibration methods dealing with the linearization of gun output are also discussed.     

Competition for consciousness among visual events: the psychophysics of reentrant visual processes

Advances in neuroscience implicate reentrant signaling as the predominant form of communication between brain areas. This principle was used in a series of masking experiments that defy explanation by feed-forward theories. The masking occurs when a brief display of target plus mask is continued with the mask alone. Two masking processes were found: an early process affected by physical factors such as adapting luminance and a later process affected by attentional factors such as set size. This later process is called masking by object substitution, because it occurs whenever there is a mismatch between the reentrant visual representation and the ongoing lower level activity. Iterative reentrant processing was formalized in a computational model that provides an excellent fit to the data. The model provides a more comprehensive account of all forms of visual masking than do the long-held feed-forward views based on inhibitory contour interactions.     

Programs for visual psychophysics on the Amiga: A tutorial

A typical psychophysical experiment presents a sequence of visual stimuli to an observer and collects and stores the responses for later analysis. Although computers can speed up this process, paint programs that allow one to prepare visual stimuli without programming cannot read responses from the mouse or keyboard, whereas BASIC and other programming languages that allow one to collect and store observer’s responses unfortunately cannot handle prepainted pictures. A new programming language called The Director provides the best of both worlds. Its BASIC-like commands can manipulate prepainted pictures, read responses made with the mouse and keyboard, and save these on disk for later analysis. A dozen sample programs are provided.     

A programmable,multifunction dual-channel waveform generator for visual psychophysics

This paper describes a relatively low-cost, flexible means of presenting patterns on a CRT. The design allows for a number of options, such as presentation of gratings as well as nonstandard stimuli (white noise), the summation and differentiation of outputs to create complex luminance waveforms, and the switching of information from one channel to the other. In addition, the visual pattern generator permits a number of temporal options, such as phase reversals and the ramping on and/or off of a stimulus. This device incorporates a hardware means of scaling grating contrast. Finally, our procedure for producing synchronization signals, which uses internally generated interrupt signals, allows a number of software options, such as keyboard scanning and reaction timing, without significant time losses.     

Real-time color-frame animation for visual psychophysics on the Macintosh computer

Psychophysical experiments involving moving stimuli require the rapid presentation of animated sequences of images. Although the Macintosh computer is widely used as a color graphics computer in research laboratories, its animation capabilities are generally ignored because of the speed limitations of drawing to the screen. New off-screen color graphics structures help to avoid the speed limitations so that real-time color or gray-scale visual motion stimuli may be generated. Precomputed animation frames are stored in off-screen memory and then rapidly transferred to the screen sequentially. The off-screen graphics structures may also be saved to disk in “Picture” form as “resources” for later retrieval and playback, allowing the experimenter to build in advance a collection of moving stimuli to use in future experiments. Code examples in the C programming language are provided, and the relative strengths and weaknesses of Macin-tosh color-frame animation for psychophysical experimentation are discussed.     

Memory for attended and unattended visual stimuli

Subjects were presented with lists of 'compound letters,' letters whose overall shapes were described by repeated use of replicates of other, smaller letters. In Experiment 1 subjects were asked to attend to either the overall letter or the smaller, constituent letter. At the end of list presentation, recall of all letters was required, but a postlist cue determined whether the attended or unattended letters were to be reported first. The results for four-item lists accorded with those of Martin (1978, 1980): order of report had a larger effect upon retention of attended letters than upon retention of unattended letters. The findings for three-item lists did not agree with Martin, however: first, the interaction of attention and order was weak; second, sharp recency for unattended letters was not found.

Experiment 2 required that subjects recall either in temporal pairs or by letter size. The results strongly suggest that the present paradigm does not constitute an analogue to dichotic listening. In particular, there is little evidence for a role for sensory retention of compound letters at time of recall.     

Long-term memory for elementary visual percepts: memory psychophysics of context and acquisition effects

In the first phase of each of two experiments, participants learned to associate a set of labels (i.e., consonant-vowel-consonant [CVC]) with a set of line lengths by using a paired-associate learning procedure. In the second phase of each experiment, these learned labels were used as memorial standards in the method of constant stimuli. Psychometric functions and the associated indices of discriminative performance (i.e., Weber fractions [WFs], just noticeable difference, and point of subjective equality) were then obtained for the remembered standards. In Experiment 1, WFs (i.e., the indices of memory precision) obtained with remembered standards were found to be higher (i.e., had poorer discriminability) than were WFs obtained with perceptual standards. In addition, WFs obtained with the remembered standards exhibited serial position effects (i.e., poorer discriminability for central items in the memory ensemble) and systematically varied with set size (i.e., the number of standards in the memory set), but WFs obtained with perceptual standards did not depend on serial position or set size. In Experiment 2, increasing the number of acquisition trials reduced WFs and diminished serial position effects. In addition, WFs did not vary systematically with the "physical" spacing between the standards in memory, but they did with the ordinal spacing. The results are consistent with a noisy analogue representation of remembered magnitudes, whereby central items in a memory ensemble are subject to lateral inhibition and thus reduced discriminability. Finally, presentation order effects, as defined by the classic time-order error, were observed with purely perceptual comparisons but not with comparisons involving a remembered standard. This latter finding is inconsistent with a strong form of the functional equivalence view of perception and memory.     

Fourier analysis of polar coordinate data in visual physiology and psychophysics

Techniques are presented for analyzing data collected as a function of: a circular independent variable (e.g., angle, direction, or orientation) or an independent variable which is cyclical (e.g., months of the year). The procedures are presented in a tutorial manner, emphasizing their relationship to more traditional statistics in experimental psychology.     

Similarity comparisons with remembered and perceived magnitudes: Memory psychophysics and fundamental measurement

At the outset, subjects learned to associate a label with each element in a set of perceptual magnitudes (visual extents), using traditional paired-associate learning methods. Subsequently, on some trials, subjects indicated which pair of two pairs of labels corresponded to the more similar perceptual referents, and, on other trials, they selected the more dissimilar pair. It is shown that these similarity comparisons satisfy the axioms (transitivity and intradimensional subtractivity) necessary to conclude that they are based on computation of the difference of the differences of analogue-based interval scale representations.The findings also permitted refutation of the idea that memory for elementary percepts arises from their reperception. Notably, the memory exponent was 0.697, but the perception exponent was 0.546, and the reperception idea requires that the memory exponent be the square of the perception exponent (0.546²=0.298). Symbolic distance effects and enhanced response time-based semantic congruity effects, typically found with binary comparisons, extend the range of commonalties found between perceptual and memory psychophysics.     

Software-based visual psychophysics using the Commodore Amiga with Deluxe Paint III

Often it is useful to produce visual displays that allow for pilot testing of experimental hypotheses, which let the experimenter examine effects reported by others, or which can be used for at least some serious experimentation (e.g., decrement in visual illusions with practice). The combination of the Amiga computer and Deluxe Paint III software is ideal for this purpose. The ease with which graphic displays can be produced, coupled with the new animation facility in the software, enables method-of-adjustment psychophysical experiments to be produced in a very short time. Worked examples are given, and the relative merits and shortcomings of the Amiga computer for these purposes are discussed.     

Memory scanning for words in visual images

This study attempts to replicate an experiment reported by Seamon (1972). In the present investigation, as in the study by Seamon, the scanning of short-term memory was compared when its contents were rehearsed words vs. a mental image. Memory sets were composed of either one, two, or three words. In the relational imagery group, subjects were required to form a single interactive mental scene of the entities which the memory set words represent. Nonimagery subjects were given instructions to covertly rehearse the memory set. In both groups, the usual memory set size (m) effect was obtained, i.e., reaction time (RT) increased linearly with m. Moreover, the set size effect was the same for both groups. This latter finding stands in marked contrast to the result obtained by Seamon; he found no effect of set size when subjects were given interactive imagery instructions. Because of the failure to replicate Seamon, an additional group of subjects were given imagery instructions. For this latter group, some of the procedural discrepancies between the relational imagery group of the present study and the corresponding group in Seamon’s study were resolved. Also, in this additional group, the set size effect was examined as a function of the subjects’ ratings of the quality of the images which they had formed. The same set size effect was found for this additional group, and the effect was independent of image quality.     

Memory for multiple visual ensembles in infancy

The number of individual items that can be maintained in working memory is limited. One solution to this problem is to store representations of ensembles that contain summary information about large numbers of items (e.g., the approximate number or cumulative area of a group of many items). Here we explored the developmental origins of ensemble representations by asking whether infants represent ensembles and, if so, how many at one time. We habituated 9-month-old infants to arrays containing 2, 3, or 4 spatially intermixed colored subsets of dots, then asked whether they detected a numerical change to one of the subsets or to the superset of all dots. Experiment Series 1 showed that infants detected a numerical change to 1 of the subsets when the array contained 2 subsets but not 3 or 4 subsets. Experiment Series 2 showed that infants detected a change to the superset of all dots no matter how many subsets were presented. Experiment 3 showed that infants represented both the approximate number and the cumulative surface area of these ensembles. Our results suggest that infants, like adults (Halberda, Sires, & Feigenson, 2006), can store quantitative information about 2 subsets plus the superset: a total of 3 ensembles. This converges with the known limit on the number of individual objects infants and adults can store and suggests that, throughout development, an ensemble functions much like an individual object for working memory.     

Memory and learning for visual signals in time and space

Vision is often characterized as a spatial sense, but what does that characterization imply about the relative ease of processing visual information distributed over time rather than over space? Three experiments addressed this question, using stimuli comprising random luminances. For some stimuli, individual items were presented sequentially, at 8 Hz; for other stimuli, individual items were presented simultaneously, as horizontal spatial arrays. For temporal sequences, subjects judged whether each of the last four luminances matched the corresponding luminance in the first four; for spatial arrays, they judged whether each of the right-hand four luminances matched the corresponding left-hand luminance. Overall, performance was far better with spatial presentations, even when the entire spatial array was presented for just tens of milliseconds. Experiment 2 demonstrated that there was no gain in performance from combining spatial and temporal information within a single stimulus. In a final experiment, particular spatial arrays or temporal sequences were made to recur intermittently, interspersed among, non-recurring stimuli. Performance improved steadily as particular stimulus exemplars recurred, with spatial and temporal stimuli being learned at equivalent rates. Logistic regression identified several shortcut strategies that subjects may have exploited while performing our task.     

Memory for feeding in rats' spatial and visual choice behaviour

Four experiments with mazes examined the effects of feeding upon rats' subsequent choice between spatially or visually distinct alternatives. It is concluded that rats can recall both whether any food remained at the cessation of feeding (nondepletion) and whether or not feeding was interrupted; both features can be associated with the place where they occurred. The memory of nondepleted food evokes an unlearned tendency to return to the place where it was present (“win-stay” behaviour). The memory of interruption transiently had a similar effect in naive animals but eventually exerts a more nonspecific influence, which facilitates not only win-stay learning but its opposite, win-shift. The nondepletion effect was also obtained when the alternatives were defined by a visual cue (brightness) rather than spatial location. The determinants of staying and shifting are discussed in terms of reward memory and exploration.     

Phenomenology and psychophysics

Recent philosophy of mind has tended to treat “inner” states, including both qualia and intentional states, as “theoretical posits” of either folk or scientific psychology. This article argues that phenomenology in fact plays a very different role in the most mature part of psychology, psychophysics. Methodologically, phenomenology plays a crucial role in obtaining psychophysical results. And more importantly, many psychophysical data are best interpreted as reporting relations between stimuli and phenomenological states, both qualitative and intentional. Three examples are used to argue for this thesis: the Weber–Fechner laws, the Craik-O’Brien–Cornsweet effect, and subjective contour figures. The phenomenological properties that play a role here do so in the role of data that ultimately constrain theoretical work (in this case theory of vision), and not as theoretical posits.     

Voluntary visual attention and phenomenal line length

In 1956, Fraisse, et al. reported subjects judged that lines were longer when voluntary attention was focused on the lines than when attention was distracted from the lines. In the many attempts to repeat these results, none has ascertained whether attention on reported line length was a phenomenal effect. In the present study, 46 subjects were shown as stimuli pairs of horizontal or vertical briefly flashed lines with a fixation cross placed equidistant between the lines but far from each one. A change in color of one arm of the cross was used as a cue to focus subjects' voluntary attention on one line. Analysis showed attention increased the judged length of attended lines. Since this effect of attention also occurred when subjects were absolutely certain they saw the stimulus lines differed in length, this effect indicates that attention increased the phenomenal length of the attended lines. This lengthening was quite small: it involved a maximum mean increase of about .15 in the probability of the comparative response that the attended line was longer. This effect occurred in the horizontal dimension and was almost absent in the vertical dimension. In agreement with data indicating that flashed lines expand phenomenally by activating motion detectors and that focused attention makes neural motion responses increase in amplitude, the present results suggest that focused attention makes attended lines look longer because it makes these lines expand phenomenally more rapidly.     

Evidence for word length coding during visual word recognition

In a masked priming procedure manipulating orthographic neighbourhood size, the priming word activates a number of word candidates of which the target could be one. Whether the target is one of the candidates or not determines how quickly it is recognised. However, the efficiency of lexical processing may be markedly less if all possible candidates are activated. One solution to this problem is if the visual system uses prime length information to reduce the number of candidates to a more manageable amount. Here, we investigated in two masked priming experiments whether prime length and orthographic information combine to facilitate target word recognition. In Experiment 1, we showed that the efficiency of visual word recognition is not influenced by the length of primes alone. However, when combined with orthographically related primes, word length coding is preserved. In Experiment 2, we investigated whether length priming affects recognition of short and long words differently. Results showed that only short words benefit from a same-length orthographically related prime, and that the priming effect does not generalise to longer words. These results suggest that the length of a word is not an essential feature in lexical processing, but that it can facilitate recognition by constraining the activation of orthographically related words.