LETTER SIMPLE
TO THE EDITORS
REACTION TIME AS A MEASURE OF THE TEMPORAL RESPONSE PROPERTIES OF TRANSIENT AND SUSTAINED CHANNELS’ (Received 28 August 1974; in revisedform7 February
Psychophysical findings reported by Kulikowski and Tolhurst (1973).Tolhurst (1973),and Breitmeyer and Juksz (1975) have revealed some of the response properties of transient and sustained channels in the human visual system. For instance, transient channels relative to sustained ones are characterized by a poor spatial resolution; i.e. they respond preferably to low spatial frequency stimuli. Moreover, transient channels show a relatively better temporal resolution as revealed by their greater sensitivity to flicker (Kulikowski and Tolhurst, 1973),rapid motion (Tolhurst, 1973) and abrupt stimulus onset (Breitmeyer and Julesz, 1975).These psychophysically determined response charactet%tics have their respective electrophysiological paralkls as revealed by single cell studies of the cat visual system (Fukuda and Saito. 1971; Cleland, Levick and Sanderson, 1973; EnrothCugell and Robson, 1966). Other electrophysiological indices of response properties d@rentiating transient from sustained cells are the tindings that transient channels have a shorter response latency to photic and electric stimulation of the optic nerve (Fukuda. 1973; Fukuda, Sugitani and Iwama, 1973)and that their fibres have a higher conduction speed (Fukuda. 1971; Hoffman and Stone, 1971; Cleland et al., 1973; Hoffman, 1973) than do sustained channels. The possible existence of such latency differences between transient and sustained channels in humans was investigated psychophysically by measuring the simple reaction time of two subjects to vertical sinusoidal gratings of variable spatial frequencies ranging from 0.5 to 1lQc/deg. After light adapting to a 5 ft-L, uniformly bright stimulus field generated on a Hewlett-Packard 1300A X-Y display (P31 phosphor), reaction times were measured by displaying a vertical grating for 50 msec (onset rise time and offset fall time were each approx 1msec) on the stimulus screen and requiring the subject to press a switch held in his dominant hand as soon as he saw a grating. The pressing of the switch stopped a msec-time clock whose onset was synchronized with the onset of the grating. The spatial contrast modulations of all gratings used in the first experiment was maintained at 50%. The results of the first experiment are shown separately for each subject in Fig. 1. Mean reaction time is plotted as a function of grating spatial frequency. Each point is based on 30 observations and the bars ’ The research reported in this paper was done while the author was at Bell Laboratories. U.S.A.
Murray Hill. N.J..
1975)
above or below each point indicate 1 S.E.M. Reaction time increases monotonically with spatial frequency. At low spatial frequencies of O+lGc/deg, both subjects yielded mean reaction times of approx 2OOmsec whereas the reaction time at the highest tested spatial frequency of ll-Oc/deg ranged from 300 to 35Omsec. Although these differences in reaction time may partially reflect the difkrences between response latencies and conduction speeds of low spatial frequency transient &am&s and high spatial frequency sustained channels, they also in part may be due to the fact that reaction time increases as the subjective contrast of gratings of equal physical contrast decreases with spatial frequency (Davidson, 1968). In the second experiment the physical contrasts of all test gratings were individually adjusted to match the subjective contrast of the 110 c/deg grating whose physical contrast was fixed at 66%. Figure 2 shows the mean reaction times and l/2 standard errors obtained with these gratings. It is evident that matching of subjective contrasts, although substantially reducing differences between reaction times to low and hii spatial frequency gratings, dii not completely eliminate these diinces. Both subjects again yielded a monotonic function relating increases in mean reaction time to increases in spatial frequency. --I
Fig. I. Mean reaction time to vertical sinusoidal gratings at an objective contrast of @5 as a function of spatial frequency. Vertical bars above or below individual data points represent I S.D.
1412
Letter IO the Edlmrs
-
ID KA
channel conduction route tiom the retma to thy superior colliculus. a faster transient channel conduction speed to the visual cortex and/or superior colliculus or both of these factors. Dq~t. of Ps.wholog,v. Ui~ivrrsity 01 Houston. Houston. TX 77004. U.S.A.
BKUNOG.
BR~ITMI.YEH
REFERENCES
SPATML REalmCv ~CVcrsrmBl
Fig. 2. Mean reaction time to vertical sinusoidal gratings, adjusted to have equal subjective contrasts, as a function of spatial frequency. Vertical bars above or below individual data points represent I SD.
For subject JB the reaction time increased from 215 to 29Omsec as the spatial frequency &eased from 0.5 to 114c/dcg. For subject KA the corresponding increase in reaction time was from 175 to 205 msec. Within subject analysis of variance revealed that this monotonic trend was statistically significant at the O-01 probability level. The results of both experiments suggest that in humans as well as lower animals low spatial frequency transient channels respond with a shorter latency than do high spatial frequency sustained channels. These latency differences, as measured by simple reaction time, may reflect either a shorter latency and faster conduction speed or a shorter conduction route or both found in transient channels as opposed to sustained ones. Transient channels are known to project from retina directly to superior colliculus (Hoffman. 1973) and indirectly via the lateral geniculate nucleus to the visual cortex (Hoffman and Stone, 1971) whereas sustained channels project exclusively via the lateral geniculate nucleus to the visual cortex (Hoffman, 1973). Thus, a faster mean reaction time to low spatial frequency gratings possibly reflects either a shorter and more direct transient
Breitmeyer B. and Julesz B. (1975) The role of on and off transients in determining the psychophysical spatial frequency response. Vision Res. 15. 41 l-415. Cleland B. G., Levick W. R. and Sarulerson K. J. (1973) Properties of sustained and transient ganglion cells in the cat retina. J. Physiol., Land, 220. 649-680. Davidson M. L. (1968) Perturbation approach to spatial brightness interaction in human vision. J. opt. Sot. Am. 58. 1300-1309.
Enroth-Cugell C. and Robson J. G. (1966) The contrast sensitivity of retinal ganglion cells of the cat. J. Physiol.. Land. 1%7. 51 l-552.
Fukuda Y. (1971) Receptive field organization of cat optic nerve fibers with special referenar to conduction velocity. Vision Res. 11. 209-226. Fukuda Y. (1973) Differentiation of principal celts of the rat lateral geniculate body into two groups; fast and slow cells. Expf Brain Rrsi 17. 242-260. Fukuda Y. and Saito H.-I. (1971)The relationshin between response characteristics to flicker stimulation and receptive field organization in the cat’s optic nerve fibers. Vision Res. 11, 227-240. Fukuda Y., Sugitani M. and Iwama K. (1973) Flash-evoked response of two types of prinefpal cells of the rat lateral geniculate body. Brain Res. S?. 208-212. Hofftnan K.-P. (1973) Conduction velocity in pathways from retina to superior colhculus in the cat: a corrdation with receptive field properties. J. Neurophysiol. 34. 409424. Hogman K.-P. and Stone J. (1971) Conduction velocity of alferents to cat visual cortex: a correlation with receptive field properties Brain Res. 32. 460-466. Kulikowski J. J. and Tolhurst D. J. (1973) Psychophysical evidence for sustained and transient defectors in human vision. J. Physiol.. Lad. 232. 149-162. Tolhunt D. J. (1973) Separate channels for the analysis of the shape and movement of a moving visual stimulus. J. Physiol., Land. 231. 385-402.
TO THE EDITORS
REACTION TIME AS A MEASURE OF THE TEMPORAL RESPONSE PROPERTIES OF TRANSIENT AND SUSTAINED CHANNELS’ (Received 28 August 1974; in revisedform7 February
Psychophysical findings reported by Kulikowski and Tolhurst (1973).Tolhurst (1973),and Breitmeyer and Juksz (1975) have revealed some of the response properties of transient and sustained channels in the human visual system. For instance, transient channels relative to sustained ones are characterized by a poor spatial resolution; i.e. they respond preferably to low spatial frequency stimuli. Moreover, transient channels show a relatively better temporal resolution as revealed by their greater sensitivity to flicker (Kulikowski and Tolhurst, 1973),rapid motion (Tolhurst, 1973) and abrupt stimulus onset (Breitmeyer and Julesz, 1975).These psychophysically determined response charactet%tics have their respective electrophysiological paralkls as revealed by single cell studies of the cat visual system (Fukuda and Saito. 1971; Cleland, Levick and Sanderson, 1973; EnrothCugell and Robson, 1966). Other electrophysiological indices of response properties d@rentiating transient from sustained cells are the tindings that transient channels have a shorter response latency to photic and electric stimulation of the optic nerve (Fukuda. 1973; Fukuda, Sugitani and Iwama, 1973)and that their fibres have a higher conduction speed (Fukuda. 1971; Hoffman and Stone, 1971; Cleland et al., 1973; Hoffman, 1973) than do sustained channels. The possible existence of such latency differences between transient and sustained channels in humans was investigated psychophysically by measuring the simple reaction time of two subjects to vertical sinusoidal gratings of variable spatial frequencies ranging from 0.5 to 1lQc/deg. After light adapting to a 5 ft-L, uniformly bright stimulus field generated on a Hewlett-Packard 1300A X-Y display (P31 phosphor), reaction times were measured by displaying a vertical grating for 50 msec (onset rise time and offset fall time were each approx 1msec) on the stimulus screen and requiring the subject to press a switch held in his dominant hand as soon as he saw a grating. The pressing of the switch stopped a msec-time clock whose onset was synchronized with the onset of the grating. The spatial contrast modulations of all gratings used in the first experiment was maintained at 50%. The results of the first experiment are shown separately for each subject in Fig. 1. Mean reaction time is plotted as a function of grating spatial frequency. Each point is based on 30 observations and the bars ’ The research reported in this paper was done while the author was at Bell Laboratories. U.S.A.
Murray Hill. N.J..
1975)
above or below each point indicate 1 S.E.M. Reaction time increases monotonically with spatial frequency. At low spatial frequencies of O+lGc/deg, both subjects yielded mean reaction times of approx 2OOmsec whereas the reaction time at the highest tested spatial frequency of ll-Oc/deg ranged from 300 to 35Omsec. Although these differences in reaction time may partially reflect the difkrences between response latencies and conduction speeds of low spatial frequency transient &am&s and high spatial frequency sustained channels, they also in part may be due to the fact that reaction time increases as the subjective contrast of gratings of equal physical contrast decreases with spatial frequency (Davidson, 1968). In the second experiment the physical contrasts of all test gratings were individually adjusted to match the subjective contrast of the 110 c/deg grating whose physical contrast was fixed at 66%. Figure 2 shows the mean reaction times and l/2 standard errors obtained with these gratings. It is evident that matching of subjective contrasts, although substantially reducing differences between reaction times to low and hii spatial frequency gratings, dii not completely eliminate these diinces. Both subjects again yielded a monotonic function relating increases in mean reaction time to increases in spatial frequency. --I
Fig. I. Mean reaction time to vertical sinusoidal gratings at an objective contrast of @5 as a function of spatial frequency. Vertical bars above or below individual data points represent I S.D.
1412
Letter IO the Edlmrs
-
ID KA
channel conduction route tiom the retma to thy superior colliculus. a faster transient channel conduction speed to the visual cortex and/or superior colliculus or both of these factors. Dq~t. of Ps.wholog,v. Ui~ivrrsity 01 Houston. Houston. TX 77004. U.S.A.
BKUNOG.
BR~ITMI.YEH
REFERENCES
SPATML REalmCv ~CVcrsrmBl
Fig. 2. Mean reaction time to vertical sinusoidal gratings, adjusted to have equal subjective contrasts, as a function of spatial frequency. Vertical bars above or below individual data points represent I SD.
For subject JB the reaction time increased from 215 to 29Omsec as the spatial frequency &eased from 0.5 to 114c/dcg. For subject KA the corresponding increase in reaction time was from 175 to 205 msec. Within subject analysis of variance revealed that this monotonic trend was statistically significant at the O-01 probability level. The results of both experiments suggest that in humans as well as lower animals low spatial frequency transient channels respond with a shorter latency than do high spatial frequency sustained channels. These latency differences, as measured by simple reaction time, may reflect either a shorter latency and faster conduction speed or a shorter conduction route or both found in transient channels as opposed to sustained ones. Transient channels are known to project from retina directly to superior colliculus (Hoffman. 1973) and indirectly via the lateral geniculate nucleus to the visual cortex (Hoffman and Stone, 1971) whereas sustained channels project exclusively via the lateral geniculate nucleus to the visual cortex (Hoffman, 1973). Thus, a faster mean reaction time to low spatial frequency gratings possibly reflects either a shorter and more direct transient
Breitmeyer B. and Julesz B. (1975) The role of on and off transients in determining the psychophysical spatial frequency response. Vision Res. 15. 41 l-415. Cleland B. G., Levick W. R. and Sarulerson K. J. (1973) Properties of sustained and transient ganglion cells in the cat retina. J. Physiol., Land, 220. 649-680. Davidson M. L. (1968) Perturbation approach to spatial brightness interaction in human vision. J. opt. Sot. Am. 58. 1300-1309.
Enroth-Cugell C. and Robson J. G. (1966) The contrast sensitivity of retinal ganglion cells of the cat. J. Physiol.. Land. 1%7. 51 l-552.
Fukuda Y. (1971) Receptive field organization of cat optic nerve fibers with special referenar to conduction velocity. Vision Res. 11. 209-226. Fukuda Y. (1973) Differentiation of principal celts of the rat lateral geniculate body into two groups; fast and slow cells. Expf Brain Rrsi 17. 242-260. Fukuda Y. and Saito H.-I. (1971)The relationshin between response characteristics to flicker stimulation and receptive field organization in the cat’s optic nerve fibers. Vision Res. 11, 227-240. Fukuda Y., Sugitani M. and Iwama K. (1973) Flash-evoked response of two types of prinefpal cells of the rat lateral geniculate body. Brain Res. S?. 208-212. Hofftnan K.-P. (1973) Conduction velocity in pathways from retina to superior colhculus in the cat: a corrdation with receptive field properties. J. Neurophysiol. 34. 409424. Hogman K.-P. and Stone J. (1971) Conduction velocity of alferents to cat visual cortex: a correlation with receptive field properties Brain Res. 32. 460-466. Kulikowski J. J. and Tolhurst D. J. (1973) Psychophysical evidence for sustained and transient defectors in human vision. J. Physiol.. Lad. 232. 149-162. Tolhunt D. J. (1973) Separate channels for the analysis of the shape and movement of a moving visual stimulus. J. Physiol., Land. 231. 385-402.
