Simon Cropper | University of Melbourne (original) (raw)
Uploads
Papers by Simon Cropper
Visual Perception Principles in Constellation Creation
Topics in Cognitive Science, Jan 3, 2024
Mental imagery in aesthetic appreciation and the understanding of the self and others
Psychology of Aesthetics, Creativity, and the Arts, Apr 13, 2023
Proceedings of SPIE, Jun 3, 2002
ABSTRACT Models that predict human performance on narrow classes of visual stimuli abound in the ... more ABSTRACT Models that predict human performance on narrow classes of visual stimuli abound in the vision science literature. However, the vision and the applied imaging communities need robust general-purpose, rather than narrow, computational human visual system (HVS) models to evaluate image fidelity and quality and ultimately improve imaging algorithms. Of the general-purpose early HVS models that currently exist, direct model comparisons on the same data sets are rarely made. The Modelfest group was formed several years ago to solve these and other vision modeling issues. The group has developed a database of static spatial test images with threshold data that is posted on the WEB for modellers to use in HVS model design and testing. The first phase of data collection was limited to detection thresholds for static gray scale 2D images, The current effort will extend the database to include thresholds for selected grayscale 2D spatio-temporal image sequences. In future years, the database will be extended to include discrimination (masking) for dynamic, color and gray scale image sequences. The purpose of this presentation is to invite the Electronic Imaging community to participate in this effort and to inform them of the developing data set, which is available to all interested researchers. This paper presents the display specifications, psychophysical methods and stimulus definitions for the second phase of the project, spatio-temporal detection. The threshold data will be collected by each of the authors over the next year and presented on the WEB along with the stimuli. For the final stimulus specifications, the latest results and other Modelfest group activities visit: http://neurometrics.com/projects/ or http://vision.arc.nasa.gov/modelfest/.
Vision Research, Aug 1, 1997
It has become apparent from recent work that the spatial frequency and orientation content of the... more It has become apparent from recent work that the spatial frequency and orientation content of the first-order (luminance) carrier is very important in determining the properties of a second-order (contrast) modulation of that carrier. In light of this we examined whether there was any evidence for a motion aftereffect in one-dimensional second-order patterns containing only two sinusoidal luminance components: a spatial beat. The stimuli were either I cpd luminance sinusoids or I cpd luminance beats modulating a carrier sinusoid of 5 cpd. The magnitude of any motion aftereffect, or any directionally specific effect of adaptation, was measured for all combinations of first and second-order test and adapting patterns. Both flickering and non-flickering stimuli were used. The results indicate that a motion aftereffect is only induced by first-order adapting stimuli, and likewise, is only measurable in first-order test stimuli. We find no evidence for any directionally specific effect of adaptation in second-order stimuli, whether the test is counterphased or otherwise. These results apparently conflict with recent reports of a second-order induced motion aftereffect, but are consistent with many other findings which show differences between the detection of motion for first and second-order stimuli. We conclude that the induction of a motion aftereffect for second-order stimuli is not a general result and is critically dependent upon (amongst other things) the local properties of the stimulus, including the spatial frequency and orientation content of the first-order carrier.
British Journal of Medical Psychology, Mar 10, 2020
This is the author manuscript accepted for publication and has undergone full peer review but has... more This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as
Rapid colour-specific detection of motion in human vision
Nature, 1996
The human visual system is much better at analysing the motion of luminance (black and white) pat... more The human visual system is much better at analysing the motion of luminance (black and white) patterns than it is at analysing the motion of colour patterns, especially if the pattern is presented very briefly or moves rapidly. We report here that observers reliably distinguish the direction of motion of a colour pattern presented for only 17 milliseconds, provided that the contrast is several times the threshold value (the contrast needed to detect the presence of the pattern). A control experiment, in which a static luminance 'mask' is added to the moving colour pattern, proves that discrimination of the direction of motion of these brief stimuli is colour-specific. The mask drastically impairs discrimination of the direction of motion of a luminance pattern, but it has little effect on a colour pattern. We conclude that the human visual system contains colour-specific motion-detection mechanisms that are capable of analysing very brief signals.
Journal of the Optical Society of America, Aug 1, 1998
The data presented in this paper examine the ability of observers to detect a modulation in the c... more The data presented in this paper examine the ability of observers to detect a modulation in the contrast of chromatic and luminance gratings as a function of the carrier contrast, duration, and spatial frequency. The nature of the signal underlying this ability is investigated by examining both the paradigm used to make the measurement and the effect of grating masks on performance in the tasks. The results show that observers' ability to discriminate amplitude modulation from an unmodulated carrier is dependent on carrier contrast but only up to ϳ5-8 times carrier-detection threshold. Discrimination is, however, independent of spatial frequency [10-1 cycles per degree (cpd) component-frequency range], carrier color, and, most surprisingly, stimulus duration (1000-30 ms). This set of experiments compliments data from previous papers and assimilates many of the conclusions drawn from this previous data. There is absolutely no evidence for the existence of a distortion product mediating performance under any of the current conditions, and the data seriously question whether the visual system might use such a signal even if it does exist under more extreme conditions than those used here. The evidence suggests that the visual system detects variations in both chromatic and luminance contrast by means of a mechanism operating locally upon the spatial structure of the carrier.
Vision Research, 1994
It is commonly assumed that the ability to discriminate velocity in a stimulus directly reflects ... more It is commonly assumed that the ability to discriminate velocity in a stimulus directly reflects the properties of the underlying directionally-selective mechanism. The results presented here show that this assumption is not always correct. Speed discrimination tasks over a range of base velocities were carried out for luminance gratings, chromatic gratings and contrast (beat) gratings of equivalent periodicity and contrasts. At low contrasts (0.5 log units above detection threshold), speed discrimination in luminance gratings was at least twice as good (when expressed as a Weber fraction), than in either chromatic gratings or beats. This is similar to the situation seen for tasks of direction discrimination using these sthnuli [e.g. Cropper and Derrington (1990) Perception, 19, A31]. When the stimulus contrasts were increased to 1.5 log tits above detection threshold, the ability to discriminate speed in both chromatic and beat stimuli improved to a performance level comparable to that shown for luminance gratings at all contrasts. 'Ihis effect is not seen for tasks of direction discrimination when the same increase in sthnulus contrast has little effect on the lower threshold of motion (LTM) measured for beat patterns. These results indicate that the ability to discriminate velocity in a stimulus does not necessarily directly reflect the characteristics of the ability to discriminate the direction of motion of that stimulus.
Vision Research, 1994
This paper measures the minimmn velocity required to discriminate the direction of motion (the lo... more This paper measures the minimmn velocity required to discriminate the direction of motion (the lower threshold of motion-LTM) for patterns which consisted of spatial variations in luminance, ~r~a~ci~ or l~ina~ coutrast in an attempt to ~~~ between tbe ~~~~~ Mooneyselective mechanisms. The characteristics of these patterns can be defined as ~~t~rder~Fo~r stimuli ~~~na~ and chromatic gratings) or ~o~~~er~#~Fo~er stimuli (contrast gratings or "beats"). Measurements for each pattern were made at durations ranging from 0.015 to O.% see and at contrasts of 0.5 log units above detection threshold and 1.5 log units above the threshold for detecting the stationary pattern. Observers were able to discriminate the direction of motion in lank gratings and hi& contrast chromatic gratings at alI durations above 0.015 sec. Tbe dire&on of motion of beats and low contrast chromatic gratings was inviable until they bad been presented for at least 0.12 sec. This was taken to iudicate the existence of a fast-act@ and a slow-acting system dealing with the Grst-and second-order patterns respectively. When defined on this basis, the chromatic stimulus acts as a first-order (luminance) pattern at high contrasts and a second-order (beat) pattern at low contrasts.
Lighthouse beams are often perceived as bent rather than straight, and observers sometimes infer ... more Lighthouse beams are often perceived as bent rather than straight, and observers sometimes infer that a rotating lighthouse beam originates from a "phantom lighthouse" that lies in the opposite direction from the true source of the beam. We argue that both illusions arise as a result of Bayesian inference based on natural scene statistics and support our argument by implementing a formal computational model. In addition to capturing both illusions, our model makes the novel predictions that a beam viewed from the side is perceived to bend towards the observer, and that the phantom lighthouse illusion should only emerge at a critical point at which the observer is located around 75 metres in front of the true source of a rotating lighthouse beam. Our theory therefore motivates a future line of experimental work, and contributes to a broader body of research that explains perceptual phenomena (including visual illusions) in terms of Bayesian inference.
Journal of Vision, Oct 7, 2020
The brain is a slave to sense; we see and hear things that are not there and engage in ongoing co... more The brain is a slave to sense; we see and hear things that are not there and engage in ongoing correction of these illusory experiences, commonly termed pareidolia. The current study investigates whether the predisposition to see meaning in noise is lateralized to one hemisphere or the other and how this predisposition to visual false-alarms is related to personality. Stimuli consisted of images of faces or flowers embedded in pink (1/f) noise generated through a novel process and presented in a divided-field paradigm. Right-handed undergraduates participated in a forced-choice signal-detection task where they determined whether a face or flower signal was present in a single-interval trial. Experiment 1 involved an equal ratio of signal-to-noise trials; experiment 2 provided more potential for illusionary perception with 25% signal and 75% noise trials. There was no asymmetry in the ability to discriminate signal from noise trials (measured using d) for either faces and flowers, although the response criterion (c) suggested a stronger predisposition to visual false alarms in the right visual field, and this was negatively correlated to the unusual experiences dimension of schizotypy. Counter to expectations, changing the signal-image to noise-image proportion in Experiment 2 did not change the number of false alarms for either faces and flowers, although a stronger bias was seen to the right visual field; sensitivity remained the same in both hemifields but there was a moderate positive correlation between cognitive disorganization and the bias (c) for "flower" judgements. Overall, these results were consistent with a rapid evidence-accumulation process of the kind described by a diffusion decision model mediating the task lateralized to the left-hemisphere.
Eye-movement patterns betray the task at hand in colour judgements
Journal of Vision, Sep 1, 2016
Colour and Motion: Masking Uber Alles
Journal of Vision, Aug 1, 2004
Journal of the Optical Society of America, Sep 1, 2001
We examined the effect of changing the composition of the carrier on the perception of motion in ... more We examined the effect of changing the composition of the carrier on the perception of motion in a drifting contrast envelope. Human observers were required to discriminate the direction of motion of contrast modulations of an underlying carrier as a function of temporal frequency and scaled (carrier) contrast. The carriers were modulations of both color and luminance, defined within a cardinal color space. Random-noise carriers had either binary luminance profiles or flat (gray-scale-white) or 1/f (pink) spectral power functions. Independent variables investigated were the envelope spatial frequency and temporal-drift frequency and the fundamental spatial frequency, color, and temporal-update frequency of the carrier. The results show that observers were able to discriminate correctly the direction of envelope motion for binary-noise carriers at both high (16 Hz) and low (2 Hz) temporal-drift frequencies. Changing the carrier format from binary noise to a flat (gray-scale) or 1/f amplitude profile reduced discrimination performance slightly but only in the hightemporal-frequency condition. Manipulation of the fundamental frequency of the carrier elicited no change in performance at the low temporal frequencies but produced ambiguous or reversed motion at the higher temporal frequencies as soon as the fundamental frequency was higher than the envelope modulation frequency. We found that envelope motion detection was sensitive to the structure of the carrier.
British Journal of Clinical Psychology, Nov 13, 2018
This is the author manuscript accepted for publication and has undergone full peer review but has... more This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as
Vision Research, Mar 1, 2006
This study seeks to clarify the reasons for some of the differences in the published data on chro... more This study seeks to clarify the reasons for some of the differences in the published data on chromatic motion perception, and to provide further support for the existence of a low-level motion mechanism sensitive to purely chromatic change. Observers discriminated the direction of motion of displaced sinusoidal gratings in the presence of a static grating mask (or pedestal). Each component of the stimulus was independently described in cardinal colour space and calibrated for subjective equiluminance using multiple methods. The motion structure, stimulus size, temporal frequency, contrast, relative phase and chromatic properties were all varied parametrically and the data cast in terms of predictions made by two different theoretical approaches to the test-mask combination. The vast majority of the data were well explained by a low-level motion mechanism sensitive to the motion of foveally-placed chromatic stimuli. Data consistent with either higher-level motion perception or a luminance-like signal were found outside the fovea and when the stimulus properties did not otherwise favour chromatic motion perception. There was some explanation of inconsistencies in previously published data and a strong suggestion that previous results showing pedestal-like behaviour for these stimulus combinations were a special case rather than a general result.
Mental imagery in aesthetic appreciation and the understanding of the self and others
Psychology of Aesthetics, Creativity, and the Arts
Induction of novel colour categories in a non-categorical colour space
Perception, 2004
Individual differences in the perception of time
Journal of Vision, Sep 1, 2015
The ability of subjects to identify and reproduce brief temporal intervals is influenced by many ... more The ability of subjects to identify and reproduce brief temporal intervals is influenced by many factors; stimulus-, task- or subject-based. The current study examines the role the individual's personality has upon their perception of short durations, and their metacognition of that percept. Undergraduate subjects (n=120) completed the OLIFE schizotypal personality questionnaire prior to performing a modified temporal-bisection task. In the task, subjects responded to two identical instantiations of a 4deg diameter sinusoidal grating, presented 4deg above fixation for 1.5secs in a rectangular temporal-envelope. They initiated presentation with a button-press, and released the button when they considered the stimulus to be half-way through (750msecs). Subjects were then asked to indicate their 'most accurate estimate' of the two intervals and given feedback for the latter half of the trials. The stimuli were either static or drifted, blocked into 100 stimulus pairs. From a group perspective there was a significant order effect whereby the first interval appeared to be shorter (and closer to veridical) than the second, although this effect reduced to insignificance when stimuli were drifted. Subjects had insight into their own performance, indicated by a reduced variance for the 'best estimate' compared to the 'worst' of the two; this difference increased with feedback. In terms of personality, the positive-psychotic subscales of the OLIFE were correlated with a reduced confidence in performance, but no actual performance difference, and a reduced ability to use feedback. Negative subscales only correlated with an increased ability to use the drift to improve performance. These data are explained in terms of an increased level of noise with increasing positive schizotypy having an effect upon precision rather than accuracy in the decision process. In a greater context, these data are also consistent with a fully-dimensional view of psychosis. Meeting abstract presented at VSS 2015.
Visual Perception Principles in Constellation Creation
Topics in Cognitive Science, Jan 3, 2024
Mental imagery in aesthetic appreciation and the understanding of the self and others
Psychology of Aesthetics, Creativity, and the Arts, Apr 13, 2023
Proceedings of SPIE, Jun 3, 2002
ABSTRACT Models that predict human performance on narrow classes of visual stimuli abound in the ... more ABSTRACT Models that predict human performance on narrow classes of visual stimuli abound in the vision science literature. However, the vision and the applied imaging communities need robust general-purpose, rather than narrow, computational human visual system (HVS) models to evaluate image fidelity and quality and ultimately improve imaging algorithms. Of the general-purpose early HVS models that currently exist, direct model comparisons on the same data sets are rarely made. The Modelfest group was formed several years ago to solve these and other vision modeling issues. The group has developed a database of static spatial test images with threshold data that is posted on the WEB for modellers to use in HVS model design and testing. The first phase of data collection was limited to detection thresholds for static gray scale 2D images, The current effort will extend the database to include thresholds for selected grayscale 2D spatio-temporal image sequences. In future years, the database will be extended to include discrimination (masking) for dynamic, color and gray scale image sequences. The purpose of this presentation is to invite the Electronic Imaging community to participate in this effort and to inform them of the developing data set, which is available to all interested researchers. This paper presents the display specifications, psychophysical methods and stimulus definitions for the second phase of the project, spatio-temporal detection. The threshold data will be collected by each of the authors over the next year and presented on the WEB along with the stimuli. For the final stimulus specifications, the latest results and other Modelfest group activities visit: http://neurometrics.com/projects/ or http://vision.arc.nasa.gov/modelfest/.
Vision Research, Aug 1, 1997
It has become apparent from recent work that the spatial frequency and orientation content of the... more It has become apparent from recent work that the spatial frequency and orientation content of the first-order (luminance) carrier is very important in determining the properties of a second-order (contrast) modulation of that carrier. In light of this we examined whether there was any evidence for a motion aftereffect in one-dimensional second-order patterns containing only two sinusoidal luminance components: a spatial beat. The stimuli were either I cpd luminance sinusoids or I cpd luminance beats modulating a carrier sinusoid of 5 cpd. The magnitude of any motion aftereffect, or any directionally specific effect of adaptation, was measured for all combinations of first and second-order test and adapting patterns. Both flickering and non-flickering stimuli were used. The results indicate that a motion aftereffect is only induced by first-order adapting stimuli, and likewise, is only measurable in first-order test stimuli. We find no evidence for any directionally specific effect of adaptation in second-order stimuli, whether the test is counterphased or otherwise. These results apparently conflict with recent reports of a second-order induced motion aftereffect, but are consistent with many other findings which show differences between the detection of motion for first and second-order stimuli. We conclude that the induction of a motion aftereffect for second-order stimuli is not a general result and is critically dependent upon (amongst other things) the local properties of the stimulus, including the spatial frequency and orientation content of the first-order carrier.
British Journal of Medical Psychology, Mar 10, 2020
This is the author manuscript accepted for publication and has undergone full peer review but has... more This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as
Rapid colour-specific detection of motion in human vision
Nature, 1996
The human visual system is much better at analysing the motion of luminance (black and white) pat... more The human visual system is much better at analysing the motion of luminance (black and white) patterns than it is at analysing the motion of colour patterns, especially if the pattern is presented very briefly or moves rapidly. We report here that observers reliably distinguish the direction of motion of a colour pattern presented for only 17 milliseconds, provided that the contrast is several times the threshold value (the contrast needed to detect the presence of the pattern). A control experiment, in which a static luminance 'mask' is added to the moving colour pattern, proves that discrimination of the direction of motion of these brief stimuli is colour-specific. The mask drastically impairs discrimination of the direction of motion of a luminance pattern, but it has little effect on a colour pattern. We conclude that the human visual system contains colour-specific motion-detection mechanisms that are capable of analysing very brief signals.
Journal of the Optical Society of America, Aug 1, 1998
The data presented in this paper examine the ability of observers to detect a modulation in the c... more The data presented in this paper examine the ability of observers to detect a modulation in the contrast of chromatic and luminance gratings as a function of the carrier contrast, duration, and spatial frequency. The nature of the signal underlying this ability is investigated by examining both the paradigm used to make the measurement and the effect of grating masks on performance in the tasks. The results show that observers' ability to discriminate amplitude modulation from an unmodulated carrier is dependent on carrier contrast but only up to ϳ5-8 times carrier-detection threshold. Discrimination is, however, independent of spatial frequency [10-1 cycles per degree (cpd) component-frequency range], carrier color, and, most surprisingly, stimulus duration (1000-30 ms). This set of experiments compliments data from previous papers and assimilates many of the conclusions drawn from this previous data. There is absolutely no evidence for the existence of a distortion product mediating performance under any of the current conditions, and the data seriously question whether the visual system might use such a signal even if it does exist under more extreme conditions than those used here. The evidence suggests that the visual system detects variations in both chromatic and luminance contrast by means of a mechanism operating locally upon the spatial structure of the carrier.
Vision Research, 1994
It is commonly assumed that the ability to discriminate velocity in a stimulus directly reflects ... more It is commonly assumed that the ability to discriminate velocity in a stimulus directly reflects the properties of the underlying directionally-selective mechanism. The results presented here show that this assumption is not always correct. Speed discrimination tasks over a range of base velocities were carried out for luminance gratings, chromatic gratings and contrast (beat) gratings of equivalent periodicity and contrasts. At low contrasts (0.5 log units above detection threshold), speed discrimination in luminance gratings was at least twice as good (when expressed as a Weber fraction), than in either chromatic gratings or beats. This is similar to the situation seen for tasks of direction discrimination using these sthnuli [e.g. Cropper and Derrington (1990) Perception, 19, A31]. When the stimulus contrasts were increased to 1.5 log tits above detection threshold, the ability to discriminate speed in both chromatic and beat stimuli improved to a performance level comparable to that shown for luminance gratings at all contrasts. 'Ihis effect is not seen for tasks of direction discrimination when the same increase in sthnulus contrast has little effect on the lower threshold of motion (LTM) measured for beat patterns. These results indicate that the ability to discriminate velocity in a stimulus does not necessarily directly reflect the characteristics of the ability to discriminate the direction of motion of that stimulus.
Vision Research, 1994
This paper measures the minimmn velocity required to discriminate the direction of motion (the lo... more This paper measures the minimmn velocity required to discriminate the direction of motion (the lower threshold of motion-LTM) for patterns which consisted of spatial variations in luminance, ~r~a~ci~ or l~ina~ coutrast in an attempt to ~~~ between tbe ~~~~~ Mooneyselective mechanisms. The characteristics of these patterns can be defined as ~~t~rder~Fo~r stimuli ~~~na~ and chromatic gratings) or ~o~~~er~#~Fo~er stimuli (contrast gratings or "beats"). Measurements for each pattern were made at durations ranging from 0.015 to O.% see and at contrasts of 0.5 log units above detection threshold and 1.5 log units above the threshold for detecting the stationary pattern. Observers were able to discriminate the direction of motion in lank gratings and hi& contrast chromatic gratings at alI durations above 0.015 sec. Tbe dire&on of motion of beats and low contrast chromatic gratings was inviable until they bad been presented for at least 0.12 sec. This was taken to iudicate the existence of a fast-act@ and a slow-acting system dealing with the Grst-and second-order patterns respectively. When defined on this basis, the chromatic stimulus acts as a first-order (luminance) pattern at high contrasts and a second-order (beat) pattern at low contrasts.
Lighthouse beams are often perceived as bent rather than straight, and observers sometimes infer ... more Lighthouse beams are often perceived as bent rather than straight, and observers sometimes infer that a rotating lighthouse beam originates from a "phantom lighthouse" that lies in the opposite direction from the true source of the beam. We argue that both illusions arise as a result of Bayesian inference based on natural scene statistics and support our argument by implementing a formal computational model. In addition to capturing both illusions, our model makes the novel predictions that a beam viewed from the side is perceived to bend towards the observer, and that the phantom lighthouse illusion should only emerge at a critical point at which the observer is located around 75 metres in front of the true source of a rotating lighthouse beam. Our theory therefore motivates a future line of experimental work, and contributes to a broader body of research that explains perceptual phenomena (including visual illusions) in terms of Bayesian inference.
Journal of Vision, Oct 7, 2020
The brain is a slave to sense; we see and hear things that are not there and engage in ongoing co... more The brain is a slave to sense; we see and hear things that are not there and engage in ongoing correction of these illusory experiences, commonly termed pareidolia. The current study investigates whether the predisposition to see meaning in noise is lateralized to one hemisphere or the other and how this predisposition to visual false-alarms is related to personality. Stimuli consisted of images of faces or flowers embedded in pink (1/f) noise generated through a novel process and presented in a divided-field paradigm. Right-handed undergraduates participated in a forced-choice signal-detection task where they determined whether a face or flower signal was present in a single-interval trial. Experiment 1 involved an equal ratio of signal-to-noise trials; experiment 2 provided more potential for illusionary perception with 25% signal and 75% noise trials. There was no asymmetry in the ability to discriminate signal from noise trials (measured using d) for either faces and flowers, although the response criterion (c) suggested a stronger predisposition to visual false alarms in the right visual field, and this was negatively correlated to the unusual experiences dimension of schizotypy. Counter to expectations, changing the signal-image to noise-image proportion in Experiment 2 did not change the number of false alarms for either faces and flowers, although a stronger bias was seen to the right visual field; sensitivity remained the same in both hemifields but there was a moderate positive correlation between cognitive disorganization and the bias (c) for "flower" judgements. Overall, these results were consistent with a rapid evidence-accumulation process of the kind described by a diffusion decision model mediating the task lateralized to the left-hemisphere.
Eye-movement patterns betray the task at hand in colour judgements
Journal of Vision, Sep 1, 2016
Colour and Motion: Masking Uber Alles
Journal of Vision, Aug 1, 2004
Journal of the Optical Society of America, Sep 1, 2001
We examined the effect of changing the composition of the carrier on the perception of motion in ... more We examined the effect of changing the composition of the carrier on the perception of motion in a drifting contrast envelope. Human observers were required to discriminate the direction of motion of contrast modulations of an underlying carrier as a function of temporal frequency and scaled (carrier) contrast. The carriers were modulations of both color and luminance, defined within a cardinal color space. Random-noise carriers had either binary luminance profiles or flat (gray-scale-white) or 1/f (pink) spectral power functions. Independent variables investigated were the envelope spatial frequency and temporal-drift frequency and the fundamental spatial frequency, color, and temporal-update frequency of the carrier. The results show that observers were able to discriminate correctly the direction of envelope motion for binary-noise carriers at both high (16 Hz) and low (2 Hz) temporal-drift frequencies. Changing the carrier format from binary noise to a flat (gray-scale) or 1/f amplitude profile reduced discrimination performance slightly but only in the hightemporal-frequency condition. Manipulation of the fundamental frequency of the carrier elicited no change in performance at the low temporal frequencies but produced ambiguous or reversed motion at the higher temporal frequencies as soon as the fundamental frequency was higher than the envelope modulation frequency. We found that envelope motion detection was sensitive to the structure of the carrier.
British Journal of Clinical Psychology, Nov 13, 2018
This is the author manuscript accepted for publication and has undergone full peer review but has... more This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as
Vision Research, Mar 1, 2006
This study seeks to clarify the reasons for some of the differences in the published data on chro... more This study seeks to clarify the reasons for some of the differences in the published data on chromatic motion perception, and to provide further support for the existence of a low-level motion mechanism sensitive to purely chromatic change. Observers discriminated the direction of motion of displaced sinusoidal gratings in the presence of a static grating mask (or pedestal). Each component of the stimulus was independently described in cardinal colour space and calibrated for subjective equiluminance using multiple methods. The motion structure, stimulus size, temporal frequency, contrast, relative phase and chromatic properties were all varied parametrically and the data cast in terms of predictions made by two different theoretical approaches to the test-mask combination. The vast majority of the data were well explained by a low-level motion mechanism sensitive to the motion of foveally-placed chromatic stimuli. Data consistent with either higher-level motion perception or a luminance-like signal were found outside the fovea and when the stimulus properties did not otherwise favour chromatic motion perception. There was some explanation of inconsistencies in previously published data and a strong suggestion that previous results showing pedestal-like behaviour for these stimulus combinations were a special case rather than a general result.
Mental imagery in aesthetic appreciation and the understanding of the self and others
Psychology of Aesthetics, Creativity, and the Arts
Induction of novel colour categories in a non-categorical colour space
Perception, 2004
Individual differences in the perception of time
Journal of Vision, Sep 1, 2015
The ability of subjects to identify and reproduce brief temporal intervals is influenced by many ... more The ability of subjects to identify and reproduce brief temporal intervals is influenced by many factors; stimulus-, task- or subject-based. The current study examines the role the individual's personality has upon their perception of short durations, and their metacognition of that percept. Undergraduate subjects (n=120) completed the OLIFE schizotypal personality questionnaire prior to performing a modified temporal-bisection task. In the task, subjects responded to two identical instantiations of a 4deg diameter sinusoidal grating, presented 4deg above fixation for 1.5secs in a rectangular temporal-envelope. They initiated presentation with a button-press, and released the button when they considered the stimulus to be half-way through (750msecs). Subjects were then asked to indicate their 'most accurate estimate' of the two intervals and given feedback for the latter half of the trials. The stimuli were either static or drifted, blocked into 100 stimulus pairs. From a group perspective there was a significant order effect whereby the first interval appeared to be shorter (and closer to veridical) than the second, although this effect reduced to insignificance when stimuli were drifted. Subjects had insight into their own performance, indicated by a reduced variance for the 'best estimate' compared to the 'worst' of the two; this difference increased with feedback. In terms of personality, the positive-psychotic subscales of the OLIFE were correlated with a reduced confidence in performance, but no actual performance difference, and a reduced ability to use feedback. Negative subscales only correlated with an increased ability to use the drift to improve performance. These data are explained in terms of an increased level of noise with increasing positive schizotypy having an effect upon precision rather than accuracy in the decision process. In a greater context, these data are also consistent with a fully-dimensional view of psychosis. Meeting abstract presented at VSS 2015.
Psychological Science, Vol. 33(3), pp. 354-363, 2022
Cultures around the world organise stars into constellations, or asterisms, and these groupings a... more Cultures around the world organise stars into constellations, or asterisms, and these groupings are often considered to be arbitrary and culture-specific. Yet there are striking similarities in asterisms across cultures and groupings such as Orion, the Big Dipper, the Pleiades and the Southern Cross are widely recognized across many different cultures. It has been informally suggested that these shared patterns are explained by common perceptual principles, such as the Gestalt laws of grouping, but there have been no systematic attempts to catalog asterisms that recur across cultures or to explain the perceptual basis of these groupings. Here we compile data from 27 cultures around the world to show that a simple computational model of perceptual grouping accounts for many of the recurring cross-cultural asterisms. As expected, asterisms such as Orion and the Big Dipper are common in our data, but we also find that lesser-known asterisms such as Delphinus and the head of Aries are both repeated across cultures and captured by our model. Our results suggest that basic perceptual principles account for more of the structure of asterisms across cultures than previously acknowledged and highlight ways in which specific cultures depart from this shared baseline.
The Conversation (Australia), 16 August , 2019
Almost every person throughout the existence of humankind has looked up at the night sky and seen... more Almost every person throughout the existence of humankind has looked up at the night sky and seen more than just a random scattering of light. Constellations of stars have helped us shape our own ongoing narratives and cultures-creating meaning in the sky above that guides us in our life on the ground below. Of course, we don't all see exactly the same night sky-there are subtle differences depending on where we are on the planet, what season it is, and the time of night, all of which are imbued into the meaning we construct about the stars.