Explanatory scope : Dual-channel RECOD model Chapter 5, Pages 186-218 Harsha KASI PhD student, Institute of Microsystems and Microelectronics EPFL

Explanatory scope : Dual-channel RECOD model Remember Original sustained-transient model & RECOD model share common mechanisms critical to masking Chapters 1, 2 and some additional results introduced in this chapter Scope of 2 models by representative set of findings 18 February 201918 February 2019 Explanatory scope : Dual-channel RECOD model

Explanatory scope : Dual-channel RECOD model Outline Justification for effects and experimental findings – comparison of model simulations and psychophysical experiments Explanatory power Comparisons and critiques 18 February 201918 February 2019 Explanatory scope : Dual-channel RECOD model

Paracontrast and metacontrast suppression Flicker persisted longer in the middle band Flicker persisted longer in the double white arcs Critical flicker frequency (CFF) : former ↑ latter (target) (mask) latter ↓ former (mask) (target) Paracontrast suppression Metacontrast facilitation → Metacontrast suppression ? Sherrington (1897) Piéron (1935) – not only CFF but on brightness perception as well → metacontrast suppression Metacontrast suppression (Brightness) – Faster transient activity by the lagging flash inhibiting the slower sustained response of the leading flash Paracontrast suppression (CFF) – Slower sustained activity by the first stimulus reciprocally inhibiting the faster transient (flicker) by the second stimulus 1st stimulus: higher CFF relative to the inhibited CFF of the 2nd stimulus 18 February 201918 February 2019 Explanatory scope : Dual-channel RECOD model

Transient masking effects 30-ms sinusoidal target grating at on-and offset of a 700-ms luminance flash mask (@ 54.8 cd/m2) transient mask overshoots Assume: 1.0 c/deg – low spatial frequency transient 7.8 c/deg – high spatial frequency sustained Peripheral transient activity by mask flash adds ‘noise’ to the ‘signal’ of transient channels and not sustained channels 1.0 c/deg: SNR or Weber ratio in transient channel ↓ → overshoots! 7.8 c/deg: only a sustained masking effect at mask onset or offset Green (1981) 18 February 201918 February 2019 Explanatory scope : Dual-channel RECOD model

Transient masking effects 2 Mitov et al. (1981): Overshoots inversely proportional to the spatial frequency of the grating – 2 c/deg 6 c/deg 18 c/deg Spatial frequencies at and below 6-c/deg, and with spatial frequency increase if the magnitude of transient activation decreases and that of sustained channel increases Teller et al., Matthews (1971): No overshoots with mask sizes e.g. <30’. However, with larger masks (e.g. > 60’) Low spatial frequency gratings, optimal for activating transient channels under large conditioning flash mask Breitmeyer and Julesz (1975) and Tulunay-Keesey and Bennis (1979): overshoots found in Green and Mittov’s studies depend on the rise and fall times of the mask at its on- and offsets Slowly ramped instead of abrupt on- and offsets attenuate the transient response leading to curbing the transient masking overshoots Matsumara’s (1976) work provides evidence to this ! 18 February 201918 February 2019 Explanatory scope : Dual-channel RECOD model

Contour and Surface dynamics – Unlumped p-pathway Metacontrast: Strongest at shorter SOA for the contour compared to the surface/brightness network (20 ms vs. 60 ms) Paracontrast: Contour network – a long-lasting suppression coupled with a strong suppression – SOA ~ -10 ms Surface network – Weaker long-lasting suppression and then enhancement Identical set of equations with different weightings associated with inhibitory and facilitatory processes 18 February 201918 February 2019 Explanatory scope : Dual-channel RECOD model

M/T Ratio – type B to A metacontrast Transition : mask/target energy ratio is greater than unity Difference in masking contrast thresholds Type B @ lower mask contrasts and produced by a high-gain, rapid-saturation transient-on-sustained inhibition transforms to a Type A @ high mask contrasts, produced by a low-gain linear intra-channel sustained-on-sustained inhibition superimposed on the former inter-channel inhibition 18 February 201918 February 2019 Explanatory scope : Dual-channel RECOD model

Dichoptic type A forward and backward masking Left eye Right Dichoptic type A forward masking by noise or structure is typically weaker than type A backward masking (Greenspoon and Eriksen 1968, Turvey 1973) Forward masking by structure or noise: Post-retinal transient activity can locally inhibit post-retinal sustained mask activity → less masking by integration On the contrary, backward masking: Sustained mask activity intrudes unobstructed into target’s sustained channels and @ post-retinal levels transient mask activity inhibits sustained target activity → facilitate intrusion – more masking ! Since these interactions are dichoptic, very likely exist at cortical levels 18 February 201918 February 2019 Explanatory scope : Dual-channel RECOD model

Explanatory scope : Dual-channel RECOD model Monoptic – Type A forward masking stronger than type A backward masking Integration of target and mask activities occur early – photoreceptor and post-receptor neural levels prior to the centrally located sustained-transient inhibitory interactions Type A forward and backward pattern masking as well as type B para- and metacontrast are obtained dichoptically and monoptically (Alpern 1953; Michaels and Turvey 1973, etc.) Either integration in common sustained pathways or inter-channel inhibition Type B metacontrast effects ↓ in magnitude as the spatial separation between the target and mask stimuli ↑ (Alpern 1953; Breitmeyer and Horman 1981, etc.) Spatially restricted receptive fields of sustained and transient neurons & the topographical mapping between retina to the visual cortex (Brooks and Jung, 1973) 18 February 201918 February 2019 Explanatory scope : Dual-channel RECOD model

Reaction times – contour interactions In paracontrast, reaction times (∆RT) for target localisation increase Paracontrast: Both data and model show an inverse U function Metacontrast: constant function Paracontrast: Both data and model show an inverse U function Metacontrast: constant function Change ∆RT in reaction times due to contour interactions between the target and mask as a function of SOA for two M/T contrast ratios. The middle curve corresponds to the average of the M/T=3 and M/T=1 data. Error bars represent ±1 SE of the mean. The squares are the predictions of the model. Reproduced from Ögmen et al. 2003 Paracontrast: close examination of M/T=3 and model – an inverse W function; peaks and dips shifted w.r.t each other 2 peaks in the W-shaped function – separate contributions of inter-channel sustained-on-transient inhibition and intra-channel transient-on-transient inhibition to reduce activity of the transient channels responding target 18 February 201918 February 2019 Explanatory scope : Dual-channel RECOD model

Explanatory scope : Dual-channel RECOD model Werner (1935): Metacontrast masking of a target pattern is inversely related to the orientation difference between target and mask stimuli Cortical transient as well as sustained neurons are orientation selective (Ikeda and Wright 1975; Stone and Dreher 1973) Mutual inhibition between cortical orientation-selective cells is itself orientation selective (Benvento et. al. 1972, etc.) Blurred mask does not substantially reduce metacontrast of a non-blurred target Transient channels are insensitive to high spatial frequencies and so to image blur (Growney, 1976) Single-transient paradigm (Breitmeyer and Rudd 1981): Brief mask suppresses visibility of a prolonged sustained peripheral target for several seconds Single-transient stimulus can activate transient-on-sustained inhibition, so despite the necessary 2-transient paradigm in metacontrast, contrary to Matin (1975). Activation of T-M neurons is not required, transient neuron activation by mask alone is sufficient 18 February 201918 February 2019 Explanatory scope : Dual-channel RECOD model

Target recoverability Addition of a second mask (M2) to a target (T) and primary metacontrast mask (M1) can lead to the recovery of visibility of the target Two effects: M2-T-M1 : Target visibility recovered No change in the visibility of prim. mask M1 2. T-M1-M2 : No change in target visibility A reduction in visibility of M1 Double disassociation, i.e., visibility and metacontrast masking effectiveness associated with sustained and transient responses Target recovery: M2 inhibits M1’s transient activity sustained-on-transient inhibition M1 reduced visibility : inter-channel transient-on-sustained inhibition by M2 18 February 201918 February 2019 Explanatory scope : Dual-channel RECOD model

Comparisons and Critiques Apart from explaining various effects (Chap. 2), 2 models give adequate explanation of many variations of them as well Revised version of Weisstein et al. 1975 accounts for metacontrast – transient-on-sustained inhibition of the non-recurrent forward type For paracontrast: sustained-on-transient inhibition of the non-recurrent forward type In conformance with assumption 1 of the Breitmeyer and Ganz’s model Differs in assumptions 2 and 4, which in Breitmeyer’s models states that: Paracontrast is realised via intra-channel inhibition effected in the sustained channels, rather than Weisstein’ et. al’s corresponding assumption of inter-channel, sustained-on-transition inhibition Weisstein’s model cannot adequately account for the absence of type B metacontrast when simple reaction time or detection rather than brightness perception are used as criterion responses 18 February 201918 February 2019 Explanatory scope : Dual-channel RECOD model

Comparisons and Critiques 2 Matin’s (1975) model with the sustained-transient model is not so similar in regard to required activation of T-M neurons T-M neurons → transient; T neurons → sustained Shorter response latency of T-M neurons compared with T neurons bears a similarity with the sustained-transient model This combined with the inter-channel inhibition is equivalent to the assumptions 1 and 3 of the sustained-transient model and the fast-inhibition hypothesis of Weisstein’s RECOD model Converges to sustained-transient model Incorporating recent neurophysiological findings, feedback mechanisms, proposing additional feedforward, feedback-dominant phases of operation, explicit network structure and a quantitative description that can be simulated and compared directly with the experimental data 18 February 201918 February 2019 Explanatory scope : Dual-channel RECOD model

Comparisons and Critiques 3 Feedback structure aspect of RECOD model makes it comparable to some discussed in Chap. 4 Dual-channel aspect of RECOD model makes it significantly different from: Bridgeman’s (1971, 1977, 1978) neural-network model Ganz’s (1975) trace decay-lateral inhibition model Reeves’s (1981) non-neural models None of the neural or non-neural models incorporate the distinction between transient response components and slow sustained ones which can reciprocally inhibit each other RECOD model incorporates: Feedback (recurrent) connections as in Bridgeman’s single-channel model Dual-channel structure to avoid spatiotemporal blurring that would occur in Bridgeman’s model so that perceptual dynamics can be organised as entities and can be processed individually 18 February 201918 February 2019 Explanatory scope : Dual-channel RECOD model

Explanatory scope : Dual-channel RECOD model Summary A review of psychophysical studies of spatiotemporal properties of human vision characterised by: 1. Separate pattern and movement or flicker thresholds 2. Temporal integration and persistence 3. Reaction time and effects of flicker adaptation all as a function of spatial frequency → existence of sustained/transient channels Supported well by neurophysiological evidences – two parallel afferent pathways with similar characteristics RECOD model adequately accounts for a wide range of visual masking phenomena discussed throughout this book ! 18 February 201918 February 2019 Explanatory scope : Dual-channel RECOD model

Thank you for your attention 18 February 201918 February 2019 Explanatory scope : Dual-channel RECOD model